• Russian mercenaries travel to Syria on secretive flights out of a public airport in Rostov, a city north of Moscow, according to a Reuters investigation. 
• The flights in and out of Rostov are operated by Cham Wings, a Syrian airline hit with US sanctions in 2016 for allegedly transporting pro-Assad fighters to Syria and helping Syrian military intelligence transport weapons and equipment.
• Between Jan. 5, 2017, to March 11, 2018, Cham Wings aircraft made 51 round trips, each time using Airbus A320 jets that can carry up to 180 passengers.

In a corner of the departures area at Rostov airport in southern Russia, a group of about 130 men, many of them carrying overstuffed military-style rucksacks, lined up at four check-in desks beneath screens that showed no flight number or destination.

When a Reuters reporter asked the men about their destination, one said: "We signed a piece of paper – we're not allowed to say anything. Any minute the boss will come and we'll get into trouble.

"You too," he warned.

The chartered Airbus A320 waiting on the tarmac for them had just flown in from the Syrian capital, Damascus, disgorging about 30 men with tanned faces into the largely deserted arrivals area. Most were in camouflage gear and khaki desert boots. Some were toting bags from the Damascus airport duty-free.

The men were private Russian military contractors, the latest human cargo in a secretive airlift using civilian planes to ferry military support to Syrian President Bashar al-Assad in his six-year fight against rebels, a Reuters investigation of the logistical network behind Assad's forces has uncovered.

The Airbus they flew on was just one of dozens of aircraft that once belonged to mainstream European and U.S. aviation companies, then were passed through a web of intermediary companies and offshore firms to Middle Eastern airlines subject to U.S. sanctions – moves that Washington alleges are helping Syria bypass the sanctions.

The flights in and out of Rostov, which no organization has previously documented, are operated by Cham Wings, a Syrian airline hit with U.S. sanctions in 2016 for allegedly transporting pro-Assad fighters to Syria and helping Syrian military intelligence transport weapons and equipment. The flights, which almost always land late at night, don't appear in any airport or airline timetables, and fly in from either Damascus or Latakia, a Syrian city where Russia has a military base.

The operation lays bare the gaps in the U.S. sanctions, which are designed to starve Assad and his allies in Iran's Revolutionary Guard and the Hezbollah militia of the men and materiel they need to wage their military campaign.

It also provides a glimpse of the methods used to send private Russian military contractors to Syria – a deployment the Kremlin insists does not exist. Russian officials say Moscow's presence is limited to air strikes, training of Syrian forces and small numbers of special forces troops.

Reuters reporters staked out the Rostov airport, logged the unusual flights using publicly available flight-tracking data, searched aircraft ownership registries and conducted dozens of interviews, including a meeting at a fashionable restaurant with a former Soviet marine major on a U.S. government blacklist.

Asked about the flights and the activities of Russian private military contractors in Syria, a spokesman for Russian President Vladimir Putin referred Reuters to the Defence Ministry – which didn't reply to the questions. The Syrian government also didn't reply to questions.

In response to detailed Reuters questions, Cham Wings said only that information on where it flies was available on its website.

The flights to Rostov aren't mentioned on the site. But the journeys do appear in online flight-tracking databases. Reporters traced flights between the Rostov airport and Syria from Jan. 5, 2017, to March 11, 2018. In that time, Cham Wings aircraft made 51 round trips, each time using Airbus A320 jets that can carry up to 180 passengers.

The issue of military casualties is highly sensitive in Russia, where memories linger of operations in Chechnya and Afghanistan that dragged on for years. Friends and relatives of the contractors suspect Moscow is using the private fighters in Syria because that way it can put more boots on the ground without risking regular soldiers, whose deaths have to be accounted for.

Forty-four regular Russian service personnel have died in Syria since the start of the operation there in September 2015, Russian authorities have said. A Reuters tally based on accounts from families and friends of the dead and local officials suggests that at least 40 contractors were killed between January and August 2017 alone.

One contractor killed in Syria left Russia on a date that tallies with one of the mysterious nighttime flights out of Rostov, his widow said. The death certificate issued by the Russian consulate in Damascus gave his cause of death as "haemorrhagic shock from shrapnel and bullet wounds."

Trying to choke off Assad's access to aircraft

To sustain his military campaign against rebels, Assad and his allies in Russia, Iran and the Hezbollah militia need access to civilian aircraft to fly in men and supplies. Washington has tried to choke off access to the aircraft and their parts through export restrictions on Syria and Iran and through Treasury Department sanctions blacklisting airlines in those countries. The Treasury Department has also blacklisted several companies outside Syria, accusing them of acting as middlemen.

"These actions demonstrate our resolve to target anyone who is enabling Assad and his regime," John E. Smith, director of the Treasury Department's Office of Foreign Assets Control, said in testimony to a congressional committee in November.

In recent years, dozens of planes have been registered in Ukraine to two firms, Khors and Dart, that were founded by a former Soviet marine major and his onetime military comrades, according to the Ukraine national aircraft register. The planes were then sold or leased and ended up being operated by Iranian and Syrian airlines, according to the flight-tracking data.

One of the companies, Khors, and the former marine major, Sergei Tomchani, have been on a U.S. Commerce Department blacklist since 2011 for allegedly exporting aircraft to Iran and Syria without obtaining licenses from Washington.

But in the past seven years, Khors and Dart have managed to acquire or lease 84 second-hand Airbus and Boeing aircraft by passing the aircraft through layers of non-sanctioned entities, according to information collated by Reuters from national aircraft registers. Of these 84 aircraft, at least 40 have since been used in Iran, Syria and Iraq, according to data from three flight-tracking websites, which show the routes aircraft fly and give the call sign of the company operating them.

In September, the U.S. Treasury Department added Khors and Dart to its sanctions blacklist, saying they were helping sanctioned airlines procure U.S.-made aircraft. Khors and Dart, as well as Tomchani, have denied any wrongdoing related to supplying planes to sanctioned entities.

The ownership histories of some of the aircraft tracked by Reuters showed how the U.S. restrictions on supplies to Iranian and Syrian airlines may be skirted. As the ownership skips from one country to the next, the complex paper trail masks the identity of those involved in Syria's procurement of the planes.

One of the Cham Wings Airbus A320 jets that has made the Rostov-Syria trip was, according to the Irish aircraft register, once owned by ILFC Ireland Limited, a subsidiary of Dublin-based AerCap, one of the world's biggest aircraft-leasing firms.

In January 2015, the aircraft was removed from the Irish register, said a spokesman for the Irish Aviation Authority, which administers the register. For the next two months, the aircraft, which carried the identification number EI-DXY, vanished from national registers before showing up on the aircraft register in Ukraine.

The Ukrainian register gave its new owner as Gresham Marketing Ltd, which is registered in the British Virgin Islands. The owners of the company are two Ukrainians, Viktor Romanika and Nikolai Saverchenko, according to corporate documents leaked from the Panamanian law firm Mossack Fonseca. Ukrainian business records show they are managers in small local businesses. Contacted by phone, Romanika said he knew nothing and hung up. Saverchenko couldn't be reached by phone and didn't respond to a letter delivered to the address listed for him.

In March 2015, Gresham leased EI-DXY to Dart, according to the Ukrainian aircraft register. The identification number was changed to a Ukrainian number, UR-CNU. On Aug. 20, 2015, Khors became the aircraft's operator, the register showed.

A representative of the Ukraine State Aviation Service said the register was not intended as official confirmation of ownership but that there had been no complaints about the accuracy of its information.

From April that year, the aircraft was flown by Cham Wings, according to data from the flight-tracking websites.

Gillian Culhane, a spokeswoman for AerCap, the firm whose subsidiary owned the plane in 2015, didn't respond to written questions or answer repeated phone calls seeking comment about what AerCap knew about the subsequent owners and operators of the plane. Dart and Khors didn't respond to questions about the specific aircraft.

Four lawyers specializing in U.S. export rules say that transactions involving aircraft that end up in Iran or Syria carry significant risks for Western companies supplying the planes or equipment. Even if they had no direct dealings with a sanctioned entity, the companies supplying the aircraft can face penalties or restrictions imposed by the U.S. government, the lawyers said.

The lawyers, however, said that the legal exposure for aircraft makers such as Boeing and Airbus was minimal, because the trade involves second-hand aircraft that are generally more than 20 years old, and the planes had been through a long chain of owners before ending up with operators subject to sanctions.

Two of the lawyers, including Edward J. Krauland, who leads the international regulation and compliance group at law firm Steptoe & Johnson, said U.S. export rules apply explicitly to Boeing aircraft because they're made in the United States. But they can also apply to Airbus jets because, in many cases, a substantial percentage of the components is of U.S. origin.

Boeing said in a statement: "The aircraft transactions described that are the subject of your inquiry did not involve The Boeing Company. Boeing maintains a robust overall trade control and sanctions compliance program." An Airbus spokesman said, "Airbus fully respects all applicable legal requirements with regard to transactions with countries under U.N., EU, UK and U.S. sanctions."

War-zone flights

When Reuters sent a series of questions to Khors and Dart about their activities, Tomchani, the former marine major, called the reporter within minutes.

He said he was no longer a shareholder in either firm but was acting as a consultant to them, and that the questions had been passed on to him. He invited the reporter to meet the following day at the high-end Velyur restaurant in Kiev, the Ukrainian capital.

In the 90-minute meeting, he denied providing aircraft to Iran or Syria. Instead, he said, Khors and Dart had provided aircraft to third parties, which he did not identify. Those third parties, he said, supplied the planes on to the end users.

"We did not supply aircraft to Iran," Tomchani, a man of military bearing in his late 50s, said as he sipped herbal tea. "We have nothing to do with supplying aircraft to Cham Wings."

Neither Dart nor Khors could have sold or leased aircraft to Cham Wings because they were not the owners of the aircraft, he said.

Tomchani used to serve in a marine unit of the Soviet armed forces in Vladivostok, on Russia's Pacific coast. In 1991, after quitting the military with the rank of major, he set up Khors along with two other officers in his unit. Tomchani and his partners made a living by flying Soviet-built aircraft, sold off cheap after the collapse of the Soviet Union, in war zones.

Khors flew cargoes in Angola for the Angolan government and Defence Ministry and aid agencies during its civil war. Tomchani said his companies also operated flights in Iraq after the U.S.-led invasion in 2003, transporting private security contractors.

Ukraine's register of business ownership showed that Tomchani ceased to be a shareholder in Khors after June 2010 and that he gave up his interest in Dart at some point after April 2011. He told Reuters he sold his stakes to "major businessmen," but declined to name them.

He did say, however, that the people listed at the time of the interview in Ukraine's business register as the owners of the two companies were merely proxies. One of the owners in the register was a mid-ranking Khors executive, one was an 81-year-old accountant for several Kiev firms, and another was someone with the same name and address as a librarian from Melitopol in southeast Ukraine.

According to the business register, the owner of 25 percent in Khors is someone called Vladimir Suchkov. The address listed for him in the register is No. 33, Elektrikov Street, Kiev. That's the same address as the one listed in Ukrainian government procurement documents for military unit No. A0515, which comes under the command of the Ukrainian Defence Ministry's Main Intelligence Directorate.

Tomchani said he and Suchkov were old acquaintances. "He wasn't a bad specialist," Tomchani said. "A young lad, but not bad." He said he believed Suchkov was living in Russia.

Reuters was unable to contact Suchkov. A telephone number listed for him was out of service. The Ukrainian Intelligence Directorate's acting head, Alexei Bakumenko, told Reuters that Suchkov doesn't work there.

Reuters found no evidence of any other link between the trade in aircraft and Ukraine's broader spy apparatus. Ukrainian military intelligence said it has no knowledge of the supply of aircraft to Syria, has no connection to the transport of military contractors from Russia to Syria, and hasn't cooperated with Khors, Dart or Cham Wings.

On Jan. 9 this year, Dart changed its name to Alanna, and listed a new address and founders, according to the Ukrainian business register. On March 1, a new company, Alanna Air, took over Alanna's assets and liabilities, the register showed.

Contractors come back in caskets 

Although Moscow denies it is sending private military contractors to Syria, plenty of people say that's untrue. Among them are dozens of friends and former colleagues of the fighters and people associated with the firm that recruits the men – a shadowy organization known as Wagner with no offices, not even a brass plaque on a door.

It was founded by Dmitry Utkin, a former military intelligence officer, according to people interviewed during this investigation. Its first combat role was in eastern Ukraine in support of Moscow-backed separatists, they said. Reuters was unable to contact Utkin directly. The League of Veterans of Local Conflicts, which according to Russian media has ties to Utkin, declined to pass on a message to him, saying it had no connection to the Wagner group.

Russia has 2,000 to 3,000 contractors fighting in Syria, said Yevgeny Shabayev, local leader of a paramilitary organization in Russia who is in touch with some of the men. In a single battle in February this year, about 300 contractors were either killed or wounded, according to a military doctor and two other sources familiar with the matter.

A Russian private military contractor who has been on four missions to Syria said he arrived there on board a Cham Wings flight from Rostov. The flights were the main route for transporting the contractors, said the man, who asked to be identified only by his first name, Vladimir. He said the contractors occasionally use Russian military aircraft too, when they can't all fit on the Cham Wings jets.

Two employees at Rostov airport talked to Reuters about the men on the mysterious flights to Syria.

"Our understanding is that these are contractors," said an employee who said he assisted with boarding for several of the Syria flights. He pointed to their destination, the fact there were no women among them and that they carried military-style rucksacks. He spoke on condition of anonymity, saying he wasn't authorized to speak to the media.

Reuters wasn't able to establish how many passengers were carried between Russia and Syria, and it is possible that some of those on board were not in Syria in combat roles. Some may have landed in Damascus, then flown to other destinations outside Syria.

Interviews with relatives of contractors killed in Syria also indicate the A320 flights to Rostov are used to transport Russian military contractors. The widow of one contractor killed in Syria said the last time she spoke to her husband by phone was on Jan. 21 last year – the same day, according to flight-tracking data, that a Cham Wings charter flew to Syria.

"He called on the evening of the 21st ... There were men talking and the sound of walkie-talkies. And by the 22nd he was already not reachable. Only text messages were reaching him," said the woman, who had previously visited her husband at a training camp for the contractors in southern Russia.

After he was killed, she said, his body was delivered to Russia. She received a death certificate saying he had died of "haemorrhagic shock from shrapnel and bullet wounds."

The widows of two other contractors killed in Syria described how their husbands' bodies arrived back home. Like the first widow, they spoke on condition of anonymity. They said representatives of the organization that recruited their husbands warned of repercussions if they spoke to the media.

The two contractors had been on previous combat tours, their widows said. The women said they received death certificates giving Syria as the location of death. Reuters saw the certificates: On one, the cause of death was listed as "carbonization of the body"– in other words, he burned to death. The other man bled to death from multiple shrapnel wounds, the certificate said.

One of the widows recounted conversations with her husband after he returned from his first tour of duty to Syria. He told her that Russian contractors there are often sent into the thick of the battle and are the first to enter captured towns, she said.

Syrian government forces then come into the town and raise their flags, he told her, taking credit for the victory.

SEE ALSO: It looks like Russia has thousands of troops in Syria

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• A little over a year in office, President Donald Trump's foreign policy stock is up.
• Part of that has to do with his unconventional approach to dealing with both friends and foes.
• But his tactics carry risks with them, and those wins could sour.

President Donald Trump has notched three notable foreign policy successes amid the acrimony of his first year in office, according to Ian Bremmer, president of geopolitical-risk firm Eurasia Group.

The wins hit three major hotspots — South Korea, North Korea, and Syria — but, as Bremmer explains, each comes with its own risks.

Most recently, at the end of March, senior US officials detailed the agreement reached with South Korea in principle to revise a trade deal first implemented in 2012.

Trump had slammed the previous deal as "horrible" and a "job killer," and US officials heralded the revision as "visionary and innovative."

With the new arrangement, US automakers can send up to 50,000 cars that meet US safety standards to South Korea, up from 25,000. Any cars beyond the new threshold will have to meet South Korean safety standards, which US companies say put them at a disadvantage. (No US carmaker sold more than 11,000 vehicles in South Korea in 2017.)

The revised deal also limits South Korean steel exports to the US and includes a provision preventing either country from weakening its currency to make its exports cheaper, though the latter provision lacks an enforcement mechanism.

Even with those stipulations, Bremmer said, "there are a host of regulatory tweaks that will make life easier for the US automotive industry, a change in South Korean steel-export limits that is favorable to US producers, new trucking rules that will improve us exports, and a Korean commitment to open their drug-reimbursement program to US pharmaceutical companies."

"I'd bet on it going forward," Bremmer wrote in an email newsletter earlier this week. "And I'd call the new agreement a meaningful improvement in bilateral economic ties."

Beyond economics, Bremmer said Trump has also eked out diplomatic wins in northwest Asia.

"China's decision to support a number of unanimous Security Council resolutions to stiffen sanctions against Pyongyang came on the back of direct Trump administration pressure," Bremmer wrote, "and linkage to the broader US-China relationship."

Chinese pressure also brought Kim Jong Un to the table, Bremmer said.

Trump also appears to have come out ahead in his approach to the conflict in Syria, particularly with his decision to launch limited strikes on an Syrian regime air base after Bashar Assad launched a chemical attack against civilians in spring 2017.

The strike, which came after Trump moved to bar refugees from the war-torn country from the US, was criticized as illegal and likely to be ineffective.

But, Bremmer said, "without advance bluster, the strikes put the [Syrian] regime on notice, reset a broader precedent and signaled that the Americans wouldn't tolerate prohibited weapons to be used, and showed both the Russians and Iranians that their direct military backing of Assad did not insulate his regime from American force."

Each case underscored themes in Trump's approach to policymaking and foreign affairs.

"It was a combination of Trump's spontaneity and unpredictability; his willingness to be risk-acceptant in challenging a previous status quo in policy; and his acceptance of advice on actual policy implementation from experts inside the administration," Bremmer said, "coupled with the power and influence of the United States leading other governments, friend and foe alike, to not want to be caught on the wrong side of Washington."

Risks involved in each win

This approach carries with it flaws, however.

"Miscalculations are more likely when you're willing to blow up the status quo," Bremmer wrote. "If your bluff is called, you lose significant credibility. If you're not bluffing, you've created a crisis that causes far more pain for both sides than you had anticipated or welcomed."

In dealing with North Korea and China, talks that go awry increase the potential for a US military strike, he said — "all the more so with Trump's new set of foreign-policy advisers."

Those talks are likely to happen in May, but before the sides even sit down, their prospects look dim.

Both sides have expressed interest in denuclearization. Trump has mused about it, criticizing the South Koreans for not paying the US to defend them and suggesting allies in the region develop their own nuclear deterrents. But Kim Jong Un has always mentioned denuclearization in the context of the whole peninsula, ridding it of US forces.

"To be clear, what the Americans say they want and what the North Koreans are prepared to deliver is unbridgeable," Bremmer wrote. The Trump administration's approach to proliferation elsewhere in Asia also looms over talks with Pyongyang.

"After all, if the Trump administration now rips up the terms of the Iran nuclear deal, right after it was negotiated and signed by the Obama administration — unilaterally deciding they don't like it so they're leaving — what would stop the Americans from doing the same to North Korea?" Bremmer added.

Similar peril exists in Trump's approach to Syria. Assad and his allies appear to have gained the advantage after seven years of brutal civil war. His removal looks unlikely, as Russia and Iran wield more influence, Bremmer said.

Moreover, there looks likely to be less resistance in the White House to Trump's instinct to pull out, according to Bremmer, as no one has a "winning strategy" to offer and many of Trump's supporters are hostile to US military engagement in far-off places.

"While you can argue the Americans leaving cedes Syria to the Russians and Iranians," Bremmer added, "that's been essentially true for years now."

In the background of all this are what appears to be increasingly contentious relations with Russia, with whom Trump has previously taken a hands-off approach.

The US expulsion of Russian diplomats was largely symbolic, as it didn't directly affect Moscow's economic or national-security interests, Bremmer wrote, adding that Trump himself seems to be taking a harder line, likely in response to Russian moves that challenge his leadership.

That trend, coupled with the addition of new, more hawkish advisers to Trump's staff, suggests a more muscular approach — and likely more tension.

"There's virtually no contact between the Russian ambassador and top Russian officials with the Trump administration. Everybody is skittish given the Mueller investigation," Bremmer cautioned. "It's one thing for the relationship to be adversarial but functional. It's another for there not to be an actual relationship. And that's what we're now heading into."

SEE ALSO: Mexico's former ambassador to China explains 'how China capitalizes where the United States is retreating'

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NOW WATCH: Wharton marketing professor says Trump hasn't helped America's brand and that isn't good for the economy

• Russia has created a secret airlift using civilian planes to ferry military support to Syrian President Bashar al-Assad in the Syrian Civil War, which has entered its sixth year.
• The flights almost always land late at night and don't appear in any airport or airline timetables.
• The operation — which both Russia and Syria have denied — lays bare the gaps in the US sanctions, which are designed to starve Assad and his allies of what they need to wage their campaign.

MOSCOW/KIEV (Reuters) - In a corner of the departures area at Rostov airport in southern Russia, a group of about 130 men, many of them carrying overstuffed military-style rucksacks, lined up at four check-in desks beneath screens that showed no flight number or destination.

When a Reuters reporter asked the men about their destination, one said: "We signed a piece of paper – we're not allowed to say anything. Any minute the boss will come and we'll get into trouble.

"You too," he warned.

The chartered Airbus A320 waiting on the tarmac for them had just flown in from the Syrian capital, Damascus, disgorging about 30 men with tanned faces into the largely deserted arrivals area. Most were in camouflage gear and khaki desert boots. Some were toting bags from the Damascus airport duty-free.

The men were private Russian military contractors, the latest human cargo in a secretive airlift using civilian planes to ferry military support to Syrian President Bashar al-Assad in his six-year fight against rebels, a Reuters investigation of the logistical network behind Assad's forces has uncovered.

The Airbus they flew on was just one of dozens of aircraft that once belonged to mainstream European and U.S. aviation companies, then were passed through a web of intermediary companies and offshore firms to Middle Eastern airlines subject to U.S. sanctions – moves that Washington alleges are helping Syria bypass the sanctions.

The flights in and out of Rostov, which no organization has previously documented, are operated by Cham Wings, a Syrian airline hit with U.S. sanctions in 2016 for allegedly transporting pro-Assad fighters to Syria and helping Syrian military intelligence transport weapons and equipment. The flights, which almost always land late at night, don't appear in any airport or airline timetables, and fly in from either Damascus or Latakia, a Syrian city where Russia has a military base.

The operation lays bare the gaps in the U.S. sanctions, which are designed to starve Assad and his allies in Iran's Revolutionary Guard and the Hezbollah militia of the men and materiel they need to wage their military campaign.

It also provides a glimpse of the methods used to send private Russian military contractors to Syria – a deployment the Kremlin insists does not exist. Russian officials say Moscow's presence is limited to air strikes, training of Syrian forces and small numbers of special forces troops.

Reuters reporters staked out the Rostov airport, logged the unusual flights using publicly available flight-tracking data, searched aircraft ownership registries and conducted dozens of interviews, including a meeting at a fashionable restaurant with a former Soviet marine major on a U.S. government blacklist.

Asked about the flights and the activities of Russian private military contractors in Syria, a spokesman for Russian President Vladimir Putin referred Reuters to the Defence Ministry – which didn't reply to the questions. The Syrian government also didn't reply to questions.

In response to detailed Reuters questions, Cham Wings said only that information on where it flies was available on its website.

The flights to Rostov aren't mentioned on the site. But the journeys do appear in online flight-tracking databases. Reporters traced flights between the Rostov airport and Syria from Jan. 5, 2017, to March 11, 2018. In that time, Cham Wings aircraft made 51 round trips, each time using Airbus A320 jets that can carry up to 180 passengers.

The issue of military casualties is highly sensitive in Russia, where memories linger of operations in Chechnya and Afghanistan that dragged on for years. Friends and relatives of the contractors suspect Moscow is using the private fighters in Syria because that way it can put more boots on the ground without risking regular soldiers, whose deaths have to be accounted for.

Forty-four regular Russian service personnel have died in Syria since the start of the operation there in September 2015, Russian authorities have said. A Reuters tally based on accounts from families and friends of the dead and local officials suggests that at least 40 contractors were killed between January and August 2017 alone.

One contractor killed in Syria left Russia on a date that tallies with one of the mysterious nighttime flights out of Rostov, his widow said. The death certificate issued by the Russian consulate in Damascus gave his cause of death as "haemorrhagic shock from shrapnel and bullet wounds."

Trying to choke off Assad's access to aircraft

To sustain his military campaign against rebels, Assad and his allies in Russia, Iran and the Hezbollah militia need access to civilian aircraft to fly in men and supplies.

Washington has tried to choke off access to the aircraft and their parts through export restrictions on Syria and Iran and through Treasury Department sanctions blacklisting airlines in those countries. The Treasury Department has also blacklisted several companies outside Syria, accusing them of acting as middlemen.

"These actions demonstrate our resolve to target anyone who is enabling Assad and his regime," John E. Smith, director of the Treasury Department's Office of Foreign Assets Control, said in testimony to a congressional committee in November.

In recent years, dozens of planes have been registered in Ukraine to two firms, Khors and Dart, that were founded by a former Soviet marine major and his onetime military comrades, according to the Ukraine national aircraft register. The planes were then sold or leased and ended up being operated by Iranian and Syrian airlines, according to the flight-tracking data.

One of the companies, Khors, and the former marine major, Sergei Tomchani, have been on a U.S. Commerce Department blacklist since 2011 for allegedly exporting aircraft to Iran and Syria without obtaining licenses from Washington.

But in the past seven years, Khors and Dart have managed to acquire or lease 84 second-hand Airbus and Boeing aircraft by passing the aircraft through layers of non-sanctioned entities, according to information collated by Reuters from national aircraft registers. Of these 84 aircraft, at least 40 have since been used in Iran, Syria and Iraq, according to data from three flight-tracking websites, which show the routes aircraft fly and give the call sign of the company operating them.

In September, the U.S. Treasury Department added Khors and Dart to its sanctions blacklist, saying they were helping sanctioned airlines procure U.S.-made aircraft. Khors and Dart, as well as Tomchani, have denied any wrongdoing related to supplying planes to sanctioned entities.

The ownership histories of some of the aircraft tracked by Reuters showed how the U.S. restrictions on supplies to Iranian and Syrian airlines may be skirted. As the ownership skips from one country to the next, the complex paper trail masks the identity of those involved in Syria's procurement of the planes.

One of the Cham Wings Airbus A320 jets that has made the Rostov-Syria trip was, according to the Irish aircraft register, once owned by ILFC Ireland Limited, a subsidiary of Dublin-based AerCap, one of the world's biggest aircraft-leasing firms.

In January 2015, the aircraft was removed from the Irish register, said a spokesman for the Irish Aviation Authority, which administers the register. For the next two months, the aircraft, which carried the identification number EI-DXY, vanished from national registers before showing up on the aircraft register in Ukraine.

The Ukrainian register gave its new owner as Gresham Marketing Ltd, which is registered in the British Virgin Islands. The owners of the company are two Ukrainians, Viktor Romanika and Nikolai Saverchenko, according to corporate documents leaked from the Panamanian law firm Mossack Fonseca. Ukrainian business records show they are managers in small local businesses. Contacted by phone, Romanika said he knew nothing and hung up. Saverchenko couldn't be reached by phone and didn't respond to a letter delivered to the address listed for him.

In March 2015, Gresham leased EI-DXY to Dart, according to the Ukrainian aircraft register. The identification number was changed to a Ukrainian number, UR-CNU. On Aug. 20, 2015, Khors became the aircraft's operator, the register showed.

A representative of the Ukraine State Aviation Service said the register was not intended as official confirmation of ownership but that there had been no complaints about the accuracy of its information.

From April that year, the aircraft was flown by Cham Wings, according to data from the flight-tracking websites.

Gillian Culhane, a spokeswoman for AerCap, the firm whose subsidiary owned the plane in 2015, didn't respond to written questions or answer repeated phone calls seeking comment about what AerCap knew about the subsequent owners and operators of the plane. Dart and Khors didn't respond to questions about the specific aircraft.

Four lawyers specializing in U.S. export rules say that transactions involving aircraft that end up in Iran or Syria carry significant risks for Western companies supplying the planes or equipment. Even if they had no direct dealings with a sanctioned entity, the companies supplying the aircraft can face penalties or restrictions imposed by the U.S. government, the lawyers said.

The lawyers, however, said that the legal exposure for aircraft makers such as Boeing and Airbus was minimal, because the trade involves second-hand aircraft that are generally more than 20 years old, and the planes had been through a long chain of owners before ending up with operators subject to sanctions.

Two of the lawyers, including Edward J. Krauland, who leads the international regulation and compliance group at law firm Steptoe & Johnson, said U.S. export rules apply explicitly to Boeing aircraft because they're made in the United States. But they can also apply to Airbus jets because, in many cases, a substantial percentage of the components is of U.S. origin.

Boeing said in a statement: "The aircraft transactions described that are the subject of your inquiry did not involve The Boeing Company. Boeing maintains a robust overall trade control and sanctions compliance program." An Airbus spokesman said, "Airbus fully respects all applicable legal requirements with regard to transactions with countries under U.N., EU, UK and U.S. sanctions."

War-zone flights

When Reuters sent a series of questions to Khors and Dart about their activities, Tomchani, the former marine major, called the reporter within minutes.

He said he was no longer a shareholder in either firm but was acting as a consultant to them, and that the questions had been passed on to him. He invited the reporter to meet the following day at the high-end Velyur restaurant in Kiev, the Ukrainian capital.

In the 90-minute meeting, he denied providing aircraft to Iran or Syria. Instead, he said, Khors and Dart had provided aircraft to third parties, which he did not identify. Those third parties, he said, supplied the planes on to the end users.

"We did not supply aircraft to Iran," Tomchani, a man of military bearing in his late 50s, said as he sipped herbal tea. "We have nothing to do with supplying aircraft to Cham Wings."

Neither Dart nor Khors could have sold or leased aircraft to Cham Wings because they were not the owners of the aircraft, he said.

Tomchani used to serve in a marine unit of the Soviet armed forces in Vladivostok, on Russia's Pacific coast. In 1991, after quitting the military with the rank of major, he set up Khors along with two other officers in his unit. Tomchani and his partners made a living by flying Soviet-built aircraft, sold off cheap after the collapse of the Soviet Union, in war zones.

Khors flew cargoes in Angola for the Angolan government and Defence Ministry and aid agencies during its civil war. Tomchani said his companies also operated flights in Iraq after the U.S.-led invasion in 2003, transporting private security contractors.

Ukraine's register of business ownership showed that Tomchani ceased to be a shareholder in Khors after June 2010 and that he gave up his interest in Dart at some point after April 2011. He told Reuters he sold his stakes to "major businessmen," but declined to name them.

He did say, however, that the people listed at the time of the interview in Ukraine's business register as the owners of the two companies were merely proxies. One of the owners in the register was a mid-ranking Khors executive, one was an 81-year-old accountant for several Kiev firms, and another was someone with the same name and address as a librarian from Melitopol in southeast Ukraine.

According to the business register, the owner of 25 percent in Khors is someone called Vladimir Suchkov. The address listed for him in the register is No. 33, Elektrikov Street, Kiev. That's the same address as the one listed in Ukrainian government procurement documents for military unit No. A0515, which comes under the command of the Ukrainian Defence Ministry's Main Intelligence Directorate.

Tomchani said he and Suchkov were old acquaintances. "He wasn't a bad specialist," Tomchani said. "A young lad, but not bad." He said he believed Suchkov was living in Russia.

Reuters was unable to contact Suchkov. A telephone number listed for him was out of service. The Ukrainian Intelligence Directorate's acting head, Alexei Bakumenko, told Reuters that Suchkov doesn't work there.

Reuters found no evidence of any other link between the trade in aircraft and Ukraine's broader spy apparatus. Ukrainian military intelligence said it has no knowledge of the supply of aircraft to Syria, has no connection to the transport of military contractors from Russia to Syria, and hasn't cooperated with Khors, Dart or Cham Wings.

On Jan. 9 this year, Dart changed its name to Alanna, and listed a new address and founders, according to the Ukrainian business register. On March 1, a new company, Alanna Air, took over Alanna's assets and liabilities, the register showed.

Contractors come back in caskets

Although Moscow denies it is sending private military contractors to Syria, plenty of people say that's untrue. Among them are dozens of friends and former colleagues of the fighters and people associated with the firm that recruits the men – a shadowy organization known as Wagner with no offices, not even a brass plaque on a door.

It was founded by Dmitry Utkin, a former military intelligence officer, according to people interviewed during this investigation. Its first combat role was in eastern Ukraine in support of Moscow-backed separatists, they said. Reuters was unable to contact Utkin directly. The League of Veterans of Local Conflicts, which according to Russian media has ties to Utkin, declined to pass on a message to him, saying it had no connection to the Wagner group.

Russia has 2,000 to 3,000 contractors fighting in Syria, said Yevgeny Shabayev, local leader of a paramilitary organization in Russia who is in touch with some of the men. In a single battle in February this year, about 300 contractors were either killed or wounded, according to a military doctor and two other sources familiar with the matter.

A Russian private military contractor who has been on four missions to Syria said he arrived there on board a Cham Wings flight from Rostov. The flights were the main route for transporting the contractors, said the man, who asked to be identified only by his first name, Vladimir. He said the contractors occasionally use Russian military aircraft too, when they can't all fit on the Cham Wings jets.

Two employees at Rostov airport talked to Reuters about the men on the mysterious flights to Syria.

"Our understanding is that these are contractors," said an employee who said he assisted with boarding for several of the Syria flights. He pointed to their destination, the fact there were no women among them and that they carried military-style rucksacks. He spoke on condition of anonymity, saying he wasn't authorized to speak to the media.

Reuters wasn't able to establish how many passengers were carried between Russia and Syria, and it is possible that some of those on board were not in Syria in combat roles. Some may have landed in Damascus, then flown to other destinations outside Syria.

Interviews with relatives of contractors killed in Syria also indicate the A320 flights to Rostov are used to transport Russian military contractors. The widow of one contractor killed in Syria said the last time she spoke to her husband by phone was on Jan. 21 last year – the same day, according to flight-tracking data, that a Cham Wings charter flew to Syria.

"He called on the evening of the 21st ... There were men talking and the sound of walkie-talkies. And by the 22nd he was already not reachable. Only text messages were reaching him," said the woman, who had previously visited her husband at a training camp for the contractors in southern Russia.

After he was killed, she said, his body was delivered to Russia. She received a death certificate saying he had died of "haemorrhagic shock from shrapnel and bullet wounds."

The widows of two other contractors killed in Syria described how their husbands' bodies arrived back home. Like the first widow, they spoke on condition of anonymity. They said representatives of the organization that recruited their husbands warned of repercussions if they spoke to the media.

The two contractors had been on previous combat tours, their widows said. The women said they received death certificates giving Syria as the location of death. Reuters saw the certificates: On one, the cause of death was listed as "carbonization of the body"– in other words, he burned to death. The other man bled to death from multiple shrapnel wounds, the certificate said.

One of the widows recounted conversations with her husband after he returned from his first tour of duty to Syria. He told her that Russian contractors there are often sent into the thick of the battle and are the first to enter captured towns, she said.

Syrian government forces then come into the town and raise their flags, he told her, taking credit for the victory.

(Additional reporting by Christian Lowe, Anton Zverev, Gleb Stolyarov and Denis Pinchuk in Moscow and Joel Schectman and Lesley Wroughton in Washington; editing by Kari Howard and Richard Woods)

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• At least 40 people were killed and hundreds more were injured from a suspected chemical attack in Syria on Saturday.
• Several unverified images and videos have been posted on social media show dozens of dead civilians with white foam coming out of their noses and mouths.
• The US State Department and local rescue groups have blamed the Syrian regime.

Dozens were brutally killed and hundreds more were injured from a suspected chemical attack in Syria on Saturday.

At least 70 people "suffocated to death" and hundreds more were injured in Douma, a suburb of Damascus in the Eastern Ghouta area, the BBC and Al Jazeera reported, citing the White Helmets and other local rescue groups.

A pro-opposition group called the Ghouta Media Center said the attack was carried out by a helicopter, which dropped a barrel bomb containing sarin gas, the BBC reported. Estimates of the death toll range from about 40 to more than 150.

"Reports from a number of contacts and medical personnel on the ground indicate a potentially high number of casualties, including among families hiding in shelters," The US State Department said in a statement late Saturday night.

Several very graphic images and videos have been posted on social media showing dozens of dead civilians with white foam coming out of their noses and mouths.

A few videos show rooms full of dead women and children who had been hiding in basements from Russian and Syrian regime airstrikes. One disturbing video shows rescue workers aiding a young girl who is choking and screaming.

The "fatalities occurred not just underground, but above ground - suggesting potent chlorine (which sinks) is now a less likely culprit," Charles Lister, a senior fellow at the Middle East Institute, tweeted.

The US State Department said Syrian President Bashar al-Assad's regime's "history of using chemical weapons against its own people is not in dispute," and referenced a sarin gas attack that Assad's forces conducted on April 4, 2017 in Khan Sheikhoun, which killed at least 70 people.

The Syrian regime has denied the accusations, blaming opposition rebels for that attack.

The attack in Douma on Saturday came one year after President Donald Trump responded to the sarin gas attack on Khan Sheikhoun by firing 59 Tomahawk cruise missiles at Syrian regime forces.

"The Assad regime and its backers must be held accountable and any further attacks prevented immediately," the State Department said. "Russia, with its unwavering support for the regime, ultimately bears responsibility for these brutal attacks, targeting of countless civilians, and the suffocation of Syria’s most vulnerable communities with chemical weapons. By shielding its ally Syria, Russia has breached its commitments to the United Nations as a framework guarantor. It has betrayed the Chemical Weapons Convention and UN Security Council Resolution 2118."

Russia "refuted the information," dismissing the news, Reuters reported.

"Make no mistake, in addition to being yet another act of sheer brutality, this was undoubtedly intended - in part - as a test of Western resolve in #Syria," Lister tweeted.

Syrian and Russian airstrikes in Eastern Ghouta have killed more than 1,600 civilians since February 18, according to AFP.

Trump tweeted about the attack Sunday morning:

"Many dead, including women and children, in mindless CHEMICAL attack in Syria. Area of atrocity is in lockdown and encircled by Syrian Army, making it completely inaccessible to outside world. President Putin, Russia and Iran are responsible for backing Animal Assad. Big price.......to pay. Open area immediately for medical help and verification. Another humanitarian disaster for no reason whatsoever. SICK! ... If President Obama had crossed his stated Red Line In The Sand, the Syrian disaster would have ended long ago! Animal Assad would have been history!"

SEE ALSO: How Russian mercenaries use secret flights to travel to Syria

DON'T MISS: A deadly chemical attack in Syria in April 2017 sparked US missile strikes — here's what happened

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• Some US lawmakers have begun suggesting that President Donald Trump should respond militarily to the chemical attack in Syria on Saturday.
• Sen. Susan Collins said Trump should consider a "targeted attack" like the one he authorized last year, and Sen. Mike Rounds said he needs to "send a message once again that what he said he meant."
• Trump tweeted that "President Putin, Russia and Iran are responsible for backing Animal Assad. Big price ... to pay."

Some US lawmakers have begun suggesting that President Donald Trump should respond militarily to the suspected chemical attack in Syria on Saturday.

At least 40 people were killed and hundreds more were injured in Douma, a suburb of Damascus that's the last rebel-held city in the Eastern Ghouta area. Estimates of the death toll from what appeared to be poison gas range up to 150.

"Last time this happened, the president did a targeted attack to take out some of the facilities. That may be an option that we should consider now," Sen. Susan Collins said on CNN's "State of the Union."

After the US concluded that President Bashar al-Assad's regime was behind the April 2017 chemical attack in Khan Sheikhoun, Trump ordered a strike of 59 Tomahawk cruise missiles on Shayrat airfield and nearby military infrastructure controlled by Assad.

Sen. Mike Rounds of South Dakota said on NBC's "Meet the Press" that Trump needs to "send a message once again that what he said he meant" and "act decisively" once he knows what his options are.

"That's appropriate. It was appropriate a year ago. It would be appropriate today," Rounds said, referring to the 2017 strike. "I think we wait until the Secretary of Defense puts together his proposals, [and] he lays them in front of the president."

Putting pressure on Putin

Lawmakers also encouraged the president to put more pressure on Russian President Vladimir Putin, whose government and military have backed Assad.

"It is further reason why it is so important that the president ramp up the pressure and the sanctions on the Russian government, because, without the support of Russia, I do not believe that Assad would still be in office," Collins said.

House Speaker Paul Ryan said the attack "is a horror that cannot be tolerated by responsible nations.""The U.S. must continue to lead an international effort to hold the Assad regime and Russia accountable for their actions," the Wisconsin representative tweeted on Sunday.

The Pentagon did not immediately respond to Business Insider's request for comment on the possibility of another US strike.

Trump tweeted on Sunday that "President Putin, Russia and Iran are responsible for backing Animal Assad. Big price ... to pay."

Russia said on Sunday that military "intervention under false & fabricated pretexts in Syria, where Russian servicemen stay at the request of the legitimate government, is absolutely unacceptable and may trigger the gravest consequences,"according to Washington Post Beirut bureau chief, Liz Sly.

"We cannot avert our eyes," Sen. Richard Blumenthal of Connecticut tweeted on Sunday. "Time to confront this horrific crisis with action ... Time for real leadership from Trump. More than merely words, action is necessary to hold Russia, as well as Syria & Iran, accountable."

SEE ALSO: Trump calls out Putin by name after at least 40 'suffocated to death' and hundreds more injured in suspected chemical attack in Syria

DON'T MISS: A deadly chemical attack in Syria in April 2017 sparked US missile strikes — here's what happened

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• President Donald Trump called Russian President Vladimir Putin out on Twitter Sunday after a suspected chemical attack in Syria killed at least 40 people.
• Ian Bremmer told Business Insider on Sunday that the US will probably soon strike Syrian forces if it can confirm that chemical weapons were indeed used.
• Lawmakers are encouraging Trump to act, and hold Syrian President Bashar al-Assad accountable for his actions.
• Bremmer also said he agrees with the potential strikes, but also says there are downsides to the proposition.

After months of praise — calling him "smart", congratulating his reelection, floating forming a "Cyber Security unit"— President Donald Trump finally called out Russian President Vladimir Putin by name on Twitter Sunday for the first time since taking office.

Trump placed part of the blame on Putin for the suspected chemical attack that killed at least 40 people in Douma, Syria on Saturday. Putin's government has backed Syrian government forces for years, while the US has sided with the opposition rebels.

"President Putin, Russia and Iran are responsible for backing Animal Assad," Trump tweeted, referring to Russia's support of Syrian President Bashar al-Assad. "Big price ... to pay."

Ian Bremmer, president of geopolitical-risk firm Eurasia Group, said that if the US can get confirmation that chemical weapons were indeed used, Trump will probably order a strike like he did in April 2017 after the US concluded Assad's regime was behind another chemical attack.

"I think he's probably going to engage in strikes against Syria," Bremmer told Business Insider on Sunday. "He's made very clear both then and now that he's not going to tolerate use of chemical weapons by Assad's regime."

Lawmakers from both parties have encouraged Trump to make the call. Sen. John McCain of Arizona went so far as to say that Trump's pledge to withdraw US troops from Syria"emboldened Assad."

"Trump was quick to call out Assad today, along with the Russian and Iranian governments, on Twitter. The question now is whether he will do anything about it," McCain said in a statement. "The President responded decisively when Assad used chemical weapons last year. He should do so again, and demonstrate that Assad will pay a price for his war crimes."

'A defining moment'

Bremmer said Trump's "strange" unwillingness to criticize Putin, and Russia in general, finally changed on Sunday.

"None of us know why it is that Trump decided he was going to be so nice individually to Putin. It's not like he cares about being nice to people," Bremmer said. "Why was he being nice to Putin, and why is he suddenly shifting? Anyone that tells you they know the answer to that question is lying."

The Trump administration is already imposing sanctions on Russian oligarchs and entities, and has expelled dozens of Russian diplomats. Bremmer said the US could decide to impose harsher sanctions on the country, conduct cyber attacks, or even release embarrassing information on Putin.

Former President Barack Obama didn't escalate into this territory, Bremmer said, because Obama "recognized there was a potential for escalation that was quite dangerous."

Trump also criticized Obama in a follow-up tweet on Sunday, saying that his predecessor should have "Drawn A Red Line In The Sand."

"There's one thing we know is that Trump absolutely wants to show that he is the opposite of Obama," Bremmer said.

Sen. Lindsey Graham of South Carolina said on ABC's "This Week" Sunday that Trump has the opportunity to "reset the table" in Syria, and suggested bombing Assad's air force and setting up so-called safe zones to achieve peace.

"If it becomes a tweet without meaning, then he has hurt himself in North Korea. If he doesn't follow through and live up to that tweet, he's going to look weak in the eyes of Russia and Iran," Graham said. "So this is a defining moment, Mr. President. You need to follow through with that tweet. Show a resolve that Obama never did to get this right."

What the international community plans to do about Assad

"One of the few things that Trump has done in foreign policy that really the international community widely supported was the strikes that he engaged in last April," Bremmer said.

The US, along with France, the UK and other nations called for an emergency UN Security Council meeting to be held on Monday "in reference to the horrible chemical weapons attack on innocent civilians in Syria," UN Ambassador Nikki Haley tweeted Sunday afternoon.

"This is becoming all too common," Haley wrote. "Strong action is needed."

The US could partner with France in the strike directly. Bremmer said French President Emmanuel Macron "recently put out his own red lines against Assad, saying that he would strike any base that lethal chemical attacks were launched from. He said he'd do it by himself."

Bremmer said "given that Macron and Trump have both made those statements, I think strikes against Assad do make sense," adding that the US would need to be careful not to hit Russian forces.

One potential downside is that Russia could execute more cyber attacks in response, Bremmer said, which could further deteriorate relations between the US and Russia.

"We're not heading to a nuclear war with the Russians, but this is a dangerous period," Bremmer said. "If the Americans engage in direct strikes against Assad given their direct support by the Russians and the Iranians — it is a dangerous thing to do, but I do think that it's an appropriate thing to do in this environment."

SEE ALSO: There's already talk the US could respond with missile strikes after Trump accused Putin and 'Animal Assad' of being behind a chemical attack in Syria

DON'T MISS: Trump calls out Putin by name after at least 40 'suffocated to death' and hundreds more injured in suspected chemical attack in Syria

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The crisis in Syria reached new, heartbreaking heights on Tuesday when one of the most devastating chemical attacks left dozens of people — including at least 27 children — dead or critically injured.

While watching a humanitarian disaster unfold before your eyes across the world may make you feel powerless, there are some things you can do to aid the people still in Syria and the 4.8 million refugees who have fled their country since the civil war began nearly six years ago.

Here are some actions you can take to help:

SEE ALSO: The deadly chemical attack is the latest to hit Syria in 6 years of brutal civil war — here's what happened

DON'T MISS: TRUMP: Syria chemical-weapons attack crossed 'beyond a red line,' and my attitude has changed

Donate to a charity

These 13 organizations received 3 or 4 stars (out of 4) from Charity Navigator, an independent nonprofit that rates charities based on their financial management and accountability. Here are links to their websites, listed in alphabetical order:

American Refugee Committee

CARE

Catholic Relief Services

Global Hope Network International

GlobalGiving

Helping Hand for Relief and Development

International Rescue Committee

Islamic Relief USA

Mercy-USA for Aid and Development

Oxfam America

Palestine Children's Relief Fund

Save the Children

UNICEF USA

Volunteer

Your time can be even more valuable than your money.

Instead of — or in addition to — donating to a charity helping Syrian refugees, volunteer with them.

Contact any of the charities listed on the previous slide (plus find more from USAID here) and ask them how you can give your time.

You can also join Doctors Without Borders and go to Syria or a European country where refugees have fled to.

If you live in several European countries or Canada, you can also list your home as a place where Syrian refugees can stay (sort of like a free Airbnb).

Educate yourself and others

Learn more about the crisis from official sources, and educate your friends and family about what you discover. The more you know about the crisis, the more you can help.

Here is more information about the situation in Syria from the United Nations Refugee Agency and the USAID Center For International Disaster Information.

Keep up with the latest news on Business Insider's Syria page.

• A suspected chemical attack caused at least 40 people to suffocate to death, and injured hundreds more, in Syria on Saturday.
• On Sunday, US Senator John McCain criticized President Donald Trump for recently saying he is in favor of pulling US troops out of Syria. 
• McCain said the president's words "emboldened" Syrian leader Bashar al-Assad.

US Senator John McCain on Sunday criticized President Donald Trump for recently saying he is in favor of pulling US troops out of Syria.

McCain said Trump's comments, that he wants to "get out" of Syria and "bring our troops home," emboldened Syrian leader Bashar al-Assad to launch a suspected chemical attack against civilians on Saturday. 

"President Trump last week signaled to the world that the United States would prematurely withdraw from Syria," McCain, who is also the chairman of the Senate Armed Services Committee, said in a statement. 

"Bashar Assad and his Russian and Iranian backers have heard him, and emboldened by American inaction, Assad has reportedly launched another chemical attack against innocent men, women and children, this time in Douma. Initial accounts show dozens of innocent civilians, including children, have been targeted by this vicious bombardment designed to burn and choke the human body and leave victims writhing in unspeakable pain," he said.

According to reports, at least 40 people suffocated to death and hundreds more were injured from a suspected chemical attack in the rebel-held town of Douma in eastern Ghouta on Saturday. Some estimates put the death toll closer to 150.

Local pro-opposition group Ghouta Media Center said the attack was carried out by a helicopter, which dropped a barrel bomb containing sarin gas. The US State Department confirmed reports of the attack and "a potentially high number of casualties" on Saturday. 

Graphic images from the attack have been posted on social media.

President Trump was quick to call out Assad for the violence in a tweet on Sunday: "President Putin, Russia and Iran are responsible for backing Animal Assad. Big price ... to pay." It was also the first time Trump has called out Putin by name on Twitter.

In his statement, McCain acknowledged Trump's quick response on Twitter but said, "The question now is whether he will do anything about it."

McCain said the president needs to "act decisively" in his response to Assad's alleged involvement in the chemical attack, and to "demonstrate that Assad will pay a price for his war crimes."

Some US lawmakers have called on the president to respond militarily to the use of chemical weapons, and have suggested a "targeted attack" on chemical weapons facilities.

SEE ALSO: There's already talk the US could respond with missile strikes after Trump accused Putin and 'Animal Assad' of being behind a chemical attack in Syria

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NOW WATCH: Why Russia is so involved in the Syrian Civil War

• Donald Trump and French President Emmanuel Macron spoke on Sunday and agreed to coordinate a "strong, joint response" on Syria.
• Bashar al-Assad's regime in Syria is suspected of using chemical weapons that killed at least 40 civilians and injuring hundreds more on Saturday.
• Macron previously declared Syria's use of chemical weapons a "red line" and said, if ever confirmed, France "will strike" in response.

President Donald Trump and his French counterpart, Emmanuel Macron, agreed the US and France will plan a "strong, joint response" on Bashar al-Assad's regime in Syria.

The two spoke on Sunday, a day after a suspected chemical attack killed at least 40 civilians in Douma, a suburb of Damascus in the Eastern Ghouta area.

"Both leaders strongly condemned the horrific chemical weapons attacks in Syria and agreed that the Assad regime must be held accountable for its continued human rights abuses," a White House readout from the call read. "They agreed to exchange information on the nature of the attacks and coordinate a strong, joint response."

Just last month the two heads of state spoke about the implementation of a 30-day ceasefire in Syria, to allow for the transportation of humanitarian aid.

Ian Bremmer, president of geopolitical-risk firm Eurasia Group, told Business Insider earlier on Sunday that Trump may order another strike on Syria if it can confirm chemical weapons were used, as he did in April 2017.

Bremmer also predicted the US may partner with France in conducting a strike, as Macron "recently put out his own red lines against Assad, saying that he would strike any base that lethal chemical attacks were launched from. He said he'd do it by himself."

"On chemical weapons, I set a red line and I reaffirm that red line,"Macron said in February. "If we have proven evidence that chemical weapons proscribed in treaties are used, we will strike the place where they are made."

The US and France, along with other nations, called for an emergency UN Security Council meeting to be held on Monday "in reference to the horrible chemical weapons attack on innocent civilians in Syria," UN Ambassador Nikki Haley tweeted Sunday afternoon.

SEE ALSO: 'This is a dangerous period': Trump is finally calling out Putin by name, and experts are anxiously watching what he'll do next

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• Syrian state media reports that a government airfield in Syria has been hit by military airstrikes. 
• A Syrian state news agency said the US may have been behind the attack.
• The Pentagon has denied US involvement in the attack.

Syrian state media reports that a government airfield in Syria has come under fire by military airstrikes. 

According to SANA news agency, which is tied to the country's Ministry of Information, a military source said several people were injured or died in the blast. The agency said the US may have been behind the attack.

The attack reportedly occurred near the Tayfur military airbase, also known as T4, in Homs. The Syrian air defense reportedly exchanged fire, according to SANA. 

Syrian TV reported loud explosions were heard near the airbase in the early hours of Monday.

Details and footage of the alleged attack have not been independently verified.

The Pentagon denied US involvement in the attack, and said it was continuing to monitor the situation closely. 

"At this time, the Department of Defense is not conducting airstrikes in Syria. However, we continue to closely watch the situation and support the ongoing diplomatic efforts to hold those who use chemical weapons, in Syria and otherwise, accountable," said the Pentagon in a statement.

Some experts suggested Israel may have been behind the attack, although Israel has not commented on the reports.

Reports of the attack follow a suspected chemical attack on the Syrian city of Douma on Saturday, which killed and injured dozens of people. 

Both Syria and Russia have denied that a chemical attack took place, despite multiple reports and video.

On Sunday, President Donald Trump and French President Emmanuel Macron agreed to coordinate a "strong, joint response" to the escalating situation in Syria. 

President Trump was quick to call out Assad for Saturday's attack in a tweet on Sunday: "President Putin, Russia and Iran are responsible for backing Animal Assad. Big price ... to pay." 

SEE ALSO: WHITE HOUSE: US and France promise a 'strong, joint response' on Syria after suspected chemical attack

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• Russia and Syria have blamed Israel for a deadly missile strike on a Syrian airfield.
• Two Israeli F-15 planes struck the T-4 air base from Lebanese air space, Russia claimed.
• Israel has not commented on the accusations.
• Syrian state TV initially suggested that the US was behind the strike.
• Israel has struck Syrian army locations multiple times before, in an attempt to hit Iranian-backed militias fighting with Assad.

Russia and Syria has blamed Israel for striking a Syrian military airfield that killed and injured several people.

Syrian state TV initially said the US may have been behind the attack on the Tayfur military airbase, also known as T-4, in Homs on early Monday morning.

The accusation against the US came after President Donald Trump directly criticised Russian President Vladimir Putin and Syrian President Bashar al-Assad after a poison gas attack on the rebel-held town of Douma.

The United States denied attacking the Syrian base, and France also said its forces had not carried it out.

The Russian military, whose forces are supporting Syrian President Bashar al-Assad, said two Israeli F-15 war planes had carried out the strikes on the Syrian T-4 air base, the Interfax news agency reported.

Interfax cited the Russian Defence Ministry as saying the Israeli war planes had carried out the strikes from Lebanese air space, and that Syrian air defense systems had shot down five of eight missiles fired.

Syrian state media, citing a military source, then carried a similar report. "The Israeli aggression on the T4 airport was carried out with F-15 planes that fired several missiles from above Lebanese land," state news agency SANA said.

When asked earlier about the explosions from the air base, an Israeli spokeswoman declined to comment. Israel had no immediate comment to the Syrian and Russian military charges.

Israel has struck Syrian army locations many times in the course of the conflict, hitting convoys and bases of Iranian-backed militias that fight alongside Assad's forces.

Israel has accused Damascus of allowing Iran to set up a complex at the T-4 base to supply arms to its ally, Lebanon's Shi'ite Hezbollah.

Syrian state TV, in its initial report, said there had been casualties in what it said was a suspected U.S. missile attack on the T-4 airfield near Homs, close to the ancient city of Palmyra in central Syria. The Pentagon denied U.S. war planes were carrying out any air strikes in Syria at the present time.

"However, we continue to closely watch the situation and support the ongoing diplomatic efforts to hold those who use chemical weapons, in Syria and otherwise, accountable," it said.

Defence analysts say there are large deployments of Russian forces at the T-4 base and jets fly regular sorties from there to strike rebel-held areas.

The Syrian state broadcaster said there were several dead and wounded in the strike.

The Syrian Observatory for Human Rights, a British-based monitor, said at least 14 people were killed including some fighters of various nationalities, a reference to Iranian-backed Shi'ite militia members, mostly from Iraq, Lebanon and Iran fighting alongside the Syrian army.

Reuters could not independently verify the report.

Trump points to Putin

The Syrian opposition blamed the suspected chemical attack on Saturday in Douma on government forces.

As international officials worked to try to confirm the chemical attack, Trump took the rare step of directly criticizing Russian President Vladimir Putin in connection with the incident.

Trump said on Twitter on Sunday there would be a "big price to pay" after medical aid groups reported dozens of civilians, including many children and women, were killed by poison gas in the besieged rebel-held town.

"Many dead, including women and children, in mindless CHEMICAL attack in Syria. Area of atrocity is in lockdown and encircled by Syrian Army, making it completely inaccessible to outside world. President Putin, Russia and Iran are responsible for backing Animal Assad. Big price to pay," Trump wrote.

The Syrian government denied its forces had launched any chemical assault, while Russia, Assad's most powerful ally, called the reports fake and warned against military action on the basis of "invented and fabricated excuses".

The Syrian government launched an air and ground assault on Douma, the last rebel-held town in the eastern Ghouta district, on Friday.

French President Emmanuel Macron spoke to Trump by telephone and the two agreed they would work together to establish clear responsibility for what Macron's office said they had agreed was a confirmed chemical attack.

Macron said in February “France will strike” in the event of lethal chemical weapon attack on civilians by government forces in Syria. A French defense ministry official said on Monday France did not carry out the air strike on the T-4 base.

The medical relief organization Syrian American Medical Society (SAMS) and the civil defense service, which operates in rebel-held areas, said in a joint statement 49 people had been killed in the suspected gas attack.

One video shared by activists showed bodies of about a dozen children, women and men, some with foam at the mouth. "Douma city, April 7 ... there is a strong smell here," a voice can be heard saying.

Reuters could not independently verify the reports.

The United States launched a cruise missile strike on a Syrian air base a year ago in response to the killing of dozens of civilians in a sarin gas attack in an opposition-held town in northwest Syria. The gas attack was blamed on Assad.

U.S. government sources said Washington's assessment of the Saturday attack was that chemical weapons were used. The European Union also said evidence pointed to the use of chemical weapons by Assad's forces.

A European diplomat said Western allies would work on building a dossier based on photos, videos, witness testimony and satellite images of Syrian flights and helicopters. However gaining access to samples on the ground would be difficult.

The U.N. Security Council will meet twice on Monday following rival requests by Russia and the United States.

U.N. war crimes investigators had previously documented 33 chemical attacks in Syria, attributing 27 to the Assad government, which has repeatedly denied using the weapons.

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NOW WATCH: Why Russia is so involved in the Syrian Civil War

• Syria is suspected of a chemical attack, which may provoke a US response.
• Defense Secretary Jim Mattis said he would not rule out "anything."
• President Donald Trump warned there would be a "big price to pay."

WASHINGTON (Reuters) - U.S. Defense Secretary Jim Mattis said on Monday he would not rule out "anything" after a suspected chemical attack in Syria triggered speculation about a U.S. military response, and he piled blame on Russia for falling short on its obligations to ensure that Syria abandoned its chemical weapons capabilities.

U.S. President Donald Trump warned on Sunday there would be a "big price to pay" after aid groups said dozens of people were killed by poison gas in a besieged rebel-held town in Syria, an attack the opposition blamed on Syrian government forces.

"The first thing we have to look at is why are chemical weapons still being used at all when Russia was the framework guarantor of removing all the chemical weapons. And so, working with our allies and our partners from NATO to Qatar and elsewhere, we are going to address this issue," Mattis said before the start of a meeting with Qatar's Emir.

Mattis had been asked if the U.S. was capable of striking President Syrian President Bashar al-Assad's chemical weapons facilities.

When asked if he could rule out taking actions, like launching airstrikes against Assad, Mattis said: "I don’t rule out anything right now."

The Syrian government denied its forces had launched any chemical assault, and Russian Foreign Minister Sergei Lavrov said such allegations were false and a provocation.

U.S. government sources said Washington's assessment was that chemical weapons were used in a besieged rebel-held town in Syria, but they are still evaluating details.

Assad is believed to have secretly kept part of Syria’s chemical weapons stockpile despite a U.S.-Russian deal under which Damascus was supposed to have handed over all such weapons for destruction in 2014, officials have said in recent months

A deadly sarin attack on a rebel-held area prompted Trump to order a missile strike last year on the Shayrat air base.

(Reporting by Idrees Ali and Phil Stewart; Editing by Chizu Nomiyama and Alistair Bell)

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Saturday's suspected chemical attack in the Syrian city of Douma has reportedly killed up to 40 people and put new focus on the already seven year-long Syrian Civil War.

The conflict has reportedly claimed the lives of as many as half a million people, caused the worst refugee crisis since WWII, and destroyed so many cities and so much infrastructure that the cost to rebuild is an estimated $200 billion. 

What started as street protests turned into a civil war, and has now erupted into a war that involves dozens of nations (directly or indirectly), hundreds of armed groups, and four main sides.

Despite all that, the war continues — and shows no real signs of stopping anytime soon.

Take a look here at how the conflict unfolded:

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In the spring of 2011, a series of pro-democracy protests known as the Arab Spring were rocking countries across the Middle East. In Syria, people peacefully protested in the streets after President Bashar Assad's government arrested and tortured teenagers for writing pro-revolution graffiti on their school wall.

Source: BBC

To quell the protests, government forces started opening fire during marches and sit-ins. With hundreds of people now killed by Assad's government, the protesters who initially called for more civil liberties started demanding a total overthrow of Assad's regime.

Source: The Guardian

With no end to the violence, some former government officers formed the Free Syrian Army to support the opposition. Other armed groups with various ideologies and loyalties would also be created. As sides battled for control over major cities such as Homs and Aleppo, the fighting escalated into a full-blown civil war by the end of 2011.

Source: BBC

• El Shafee Elsheik gave a TV interview from captivity in Syria.
• He is accused of being part of the "Beatles" group of British jihadists who recorded gruesome beheading videos for ISIS.
• He calmly explained to a journalist why he liked Raqqa and supports slavery.
• Elsheik said: "just because America decided to abolish something... does not mean that every person has to run behind America and say this is now an abominable act."

One of the most notorious ISIS jihadists calmly explained why he supports ISIS practice of enslaving people in conquers, in a jailhouse interview from Syria.

El Shafee Elsheik, originally from London, has been accused of part part of a group of prison guards and executioners known as "The Beatles," who were behind some of the on-screen beheadings which became ISIS's calling card.

He gave his first on-camera interview with the news outlet Akhbar Al Aan. Its correspondent Jenan Moussa was given access to Elsheik in a prison run by the Syrian Democratic Forces.

The footage was released on Sunday, and featured Elsheik giving a limited insight into his life in Raqqa when it was under ISIS control. The exchange (in English) was posted on social media:

At some points Elsheik distanced himself from ISIS's actions, and said he could not be held personally responsible for them.

However, other aspects he endorsed, including slavery.

He said the practice was a natural part of human society, used to be part of Islam, and should not be discontinued simply because Western countries abolished it.

Elsheik, when prompted by his interviewer to denounce slavery as a practice, said:

"Do I denounce what? Slavery? I don’t denounce slavery, no.

You have to understand that just because America decided to abolish something, I don’t know what year it was, does not mean that every person has to run behind America and say this is now an abominable act that nobody can do.

"The reality is slavery is something that’s been around as long as humans have been around.

"Islamic texts have spoken about slavery and the rights of a slave, and there’s a whole jurisprudence about slavery and the rights of slaves and the rights of slave owners."

He stands accused of helping orchestrate the gruesome beheading videos which became ISIS's hallmark, under the leadership of Mohammed Emwazi, the Londoner who came to be known as Jihadi John.

Elsheik studiously avoided responding to most accusations related to executions or other specific allegations of wrongdoing while he was part of ISIS.

Just before ending the interview he denied personally beheading anybody, and said he doesn't like watching beheading videos.

However, his responses leave open the possibility he could have been involved in another way. He said he would address the accusations fully in a formal trial.

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• President Donald Trump said the alleged chemical attack in Syria over the weekend was "atrocious" and "horrible."
• Trump said a major decision from his administration was coming as early as Monday.
• Both Trump and Defense Secretary Jim Mattis said "nothing is off the table."

President Donald Trump responded to this weekend's alleged chemical attack on Monday in a press pool, striking an aggressive tone.

Trump called the attack, which left dozens dead in a rebel-held town near the Syrian capital of Damascus, "atrocious" and "horrible." His administration, Trump said, would make a decision as to how to respond within 48 hours and "probably" by Tuesday.

"This is about humanity, and it can't be allowed to happen," Trump said, adding that the US was going to find out who was responsible for the attack. "If it's the Russians, if it's Syria, if it's Iran, if it's all of them together, we'll figure it out," he said.

"We can not allow atrocities like that," he added. "Everybody's going to pay a price."

When asked what type of options were being considered, the president said "nothing is off the table." Defense Secretary Jim Mattis made the same statement earlier Monday.

Local aid groups blamed the attack on the Syrian government. The decision Monday on how to respond comes on John Bolton's first day as White House national security adviser. Bolton has been extremely hawkish in the past, especially on the key Syria ally Iran.

Earlier Monday, Syria accused Israeli warplanes of attacking a Syrian airfield in Homs province.

The airfield, known as T-4, was attacked in the past by Israeli Air Force jets after an Iranian drone violated Israeli airspace. Syrian air defenses shot down an IAF F-16 that was returning from the mission, but only after it flew back into Israeli airspace.

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• The US is contemplating retaliatory strikes in Syria after chemical-weapons attacks there this weekend.
• That decision-making process is taking place with John Bolton in his new role of national security adviser.
• Bolton is generally seen as hawkish, but how he relates to Trump and his staff remains to be seen.

John Bolton takes over as White House national security adviser on Monday, hours after chemical-weapons strikes on civilians in Syria again horrified the world.

The attacks brought reprobation upon Syrian dictator Bashar Assad, as well as on Iran and Russia, his two biggest backers. "It was atrocious. It was horrible," Trump said Monday, adding that there's "not much of a doubt" about who was responsible.

"We'll be making that decision very quickly. Probably by the end of today," Trump told reporters on Monday. But it remains unclear how the US will respond, and the outlook is further clouded by Bolton's ascension to his new post.

"It's going to be baptism by fire," Johnathan Schanzer, senior vice president at the Foundation for Defense of Democracies, a think tank with close ties to the Trump administration, told The Wall Street Journal. "It will be interesting to see whether it's the same John Bolton in the White House that we see on Fox News."

Bolton, who was US ambassador to the UN during the George W. Bush administration and a foreign-policy pundit in the years since, is known for hawkish views, particularly on Iran. (After leaving government, he advocated on behalf of Iranian opposition group Mujahedeen Khalq, or MEK, which was once labeled a terrorist group by the US.)

"As incidents in Syria and Iraq increasingly put American forces at risk, Washington should not get lost in deconfliction negotiations or modest changes in rules of engagement," Bolton said in a June 2017 column. "Instead, the Trump administration should recraft the US-led coalition to ensure that America's interests, rather than Russia's or Iran's, predominate once ISIS is defeated."

On the eve of taking office, Bolton tried to distance himself from his punditry, saying on Fox News that while he had "never been shy" about his views, "what I have said in private now is behind me."

Bolton has defined himself as an "Americanist" sworn to defend US interests and has said, in the context of stick-and-carrot diplomacy, "I don't do carrots."

A longtime adviser recently told The New York Times that Bolton — a noted critic of the UN — has said he sees diplomacy as effective in most cases. The adviser quoting Bolton as saying, "My belief is diplomatic crises, 99 and 44/100ths percent of them can be resolved with public diplomacy," making a reference to an old soap commercial.

Stepping immediately into the current crisis in Syria

Stepping immediately into office amid the current crisis in Syria will not only test Bolton's ability to advise Trump but also reveal how his management style — widely criticized as overbearing and hostile to disagreement — gels with a national security council staff that has seen considerable turnover since Trump took office, losing former chief Army Gen. H.R. McMaster and longtime spokesman Michael Anton in recent weeks.

"How much influence the NSC staff has is largely a function of the relationship between them and the national-security adviser and the decision-making style of the president," said Colin Kahl, who was deputy assistant to President Barack Obama and national security adviser to Vice President Joe Biden between 2014 and 2017.

"In this case, Bolton has signaled he intends to 'clean house' at the NSC, suggesting he has little faith in the current group," Kahl told Business Insider.

"Bolton is also notoriously harsh toward staff who don't agree with his pre-existing beliefs, suggesting he is not terribly open-minded to being persuaded by his staff," Kahl added.

Bolton's reputed disdain for those who lack his knowledge and experience could create tension with Trump son-in-law and senior adviser Jared Kushner, who has assumed a broad foreign-policy portfolio— but it may also affect his relationship with Trump, who has at times evinced little interest in the exerting required of foreign-policy decision-making.

One of Bolton's former aides told CNN that the new national security adviser was a "team player" would look to gain Trump's trust rather than pursue his own goals.

"He is going to do what President Trump tells him to do. He's going to implement the policies that President Trump wants implemented," the aide said, adding that Bolton would provide well-considered policy options that the president had previously lacked.

Peter Feaver, who overlapped with Bolton as a Bush administration national-security official, told CNN that, contrary to most assessments, Bolton would not reflexively pursue hawkish policies to the exclusion of other approaches.

"That is unfair to him," Feaver told CNN, adding that Bolton did exhibit an aversion to diplomacy in some cases.

"When you are dealing with what used to be called 'pariah regimes,' he will quickly eviscerate the the more optimistic policy proposals that presume on the other side's willingness to accept win-win solutions," Feaver said. "He will point out the flaws with those, which ends you up at the last-resort node of the decision tree. That is how he ends up being a hawk. He is not a use-force-first guy."

Trump's position on Syria, to the extent he has one, seems to be fluid. While he has pushed to leave the war-torn country in recent weeks, he responded to the latest chemical attack in Syria more aggressively, putting part of the blame on Russian President Vladimir Putin for backing Assad — a departure from his previous attitude toward Putin — and warning of a "Big price ... to pay."

'Trump and Bolton are basically aligned'

Trump has been thus far been wary of the national security council staff, "seeing them as remnants of the 'deep state,' 'Obama holdovers,' and leakers," Kahl told Business Insider. "He is more likely to listen to Bolton, however, because he and Bolton are more aligned in terms of their beliefs and style than was the case with McMaster."

It remains to be seen what specific response Bolton advocates. His comments on Syria in the past have not precluded military action against the Assad regime, but he has stressed that such action should come as part of a broader strategy.

In 2013, when Obama threatened military strikes in response to a deadly chemical weapons attack in Syria, Bolton came out against such a move, saying"the notion of a limited strike ... will not create a deterrent effect."

He voiced a similar criticism in 2017, as the Trump administration prepared for strikes against the Syrian regime in response to another chemical-weapons attack, saying any military response needed to come as part of a strategy to counter Russian and Iran. (Trump reportedly rebuffed Israeli Prime Minister Benjamin Netanyahu efforts to get him to reconsider pulling out of Syria and to act against Iran's presence in the country.)

"On the use of force, Trump and Bolton are basically aligned," Kahl said. "They believe it is important to unilaterally demonstrate US military power ... to put our adversaries on notice but without getting too deeply involved on the ground."

"Neither is a fan of diplomacy, multilateralism, international law, or nation-building," he added. "So it is all sticks, no carrots."

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• Syrian President Bashar al-Assad may have carried out a chemical attack in Douma, Syria, over failed negotiations between his regime and the main opposition group in the region, Jaysh al-Islam.
• The tactic may have worked in the short term, as Jaysh al-Islam agreed on Sunday to evacuate the area.
• While it can't be said with certainty that Assad's alleged use of chemical weapons on Saturday forced Jaysh al-Islam to evacuate the area, circumstantial evidence indicates this.

Syrian President Bashar al-Assad has reportedly used chemical weapons on his own people since at least 2013, with a number of attacks coming in the last few months.

An attack on Saturday reportedly killed at least 40 civilians and has drawn condemnation from around the world, including President Donald Trump. Immediately after reports and images from Saturday's attack emerged on social media, Russian and Syrian Assad supporters began countering allegations that the government's forces had carried out another chemical attack.

They claimed Assad had no reason to use chemical weapons, and that the Syrian government was winning the fight against the main opposition group in the region, Jaysh al-Islam. Russia even called the allegations "fake news."

But Neil Hauer, an independent analyst focusing on Russia and Syria, tweeted a response to their claims, arguing that negotiations between the regime and Jaysh al-Islam, with Russia as a guarantor, broke down on Thursday.

The regime wanted Jaysh al-Islam to either lay down their weapons or be bused out of the area to central Syria, Hauer wrote, but the negotiations faltered. Jaysh al-Islam reportedly agreed to lay down their weapons only if they were allowed to stay in Douma as a local police force, which Assad didn't favor.

As a result, the regime struck Douma hard with airstrikes on Friday, then allegedly used chemical weapons on Saturday. On Sunday, Jaysh al-Islam agreed to leave the area.

"Got it?," Hauer tweeted.

Experts agree that Assad succeeded

"That's right," Jennifer Cafarella, a senior intelligence planner at the Institute for the Study of War, told Business Insider. "Assad attacked civilian targets in Douma after Jaysh al Islam refused to accept a surrender deal."

"Assad's goal was to break the will of the local population and force Jaysh al Islam to surrender. He succeeded," Cafarella wrote in an emailed statement, adding that it was also to show "impunity after President Trump signaled his desire to withdraw from Syria."

"Is there an effort to pressure [Jaysh al-Islam] to adhere to an evacuation deal brokered by the Russians?" Emily Hawthorne, a Middle East and North Africa analyst at Stratfor, told Business Insider. "Absolutely."

"I don't know if you can [make] a direct one-to-one: chemical weapons attack on Saturday, and then a sudden adherence to the evacuation deal on Russian terms on Sunday," Hawthorne said. "That's what it looks like when you read the press reports, but unless you have a source that's within those negotiations, I just don't know if you can say with absolute certainty that the chemical attacks produced that one-to-one effect."

"But I think it's safe to say that it's a huge part of pressure tactics by the Syrian government to terrorize them," Hawthorne said.

Trump said on Monday that he would make a decision as to how to respond within 48 hours.

"This is about humanity, and it can't be allowed to happen," Trump said, adding that the US was going to find out who was responsible for the attack. "If it's the Russians, if it's Syria, if it's Iran, if it's all of them together, we'll figure it out," he said.

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• A hospital in Douma, Syria, was reportedly attacked with what may be sarin and chlorine gases on Saturday.
• Videos and photos on social media allegedly show dead men, women, and children with others foaming at the mouth and struggling to breathe.
• The suspected gas attacks reportedly killed about 40 to 150 people and injured hundreds of others.
• Sarin gas is a nerve agent that forces the body's muscles into overdrive, leading to convulsions, loss of breathing, and often death.

On Saturday night, barrel bombs filled with chlorine and sarin gases reportedly fell on and near a hospital in Douma, Syria, killing dozens of men, women, and children.

The area is held by rebel forces that oppose the Syrian regime led by Bashar al-Assad, and the timing of the attack came just days after failed negotiations with opposition groups. Al-Assad's regime has also reportedly used chemical weapons since 2013 against rebel-held enclaves packed with civilians.

Syria denied the event ever took place, and — similar to a suspected gas attack in April 2017— its ally Russia reportedly called the event "fabricated" and warned western countries not to retaliate.

However, the US State Department on Monday said the symptoms of victims "reported by credible medical professionals" and those captured in traumatic videos and photos on social media "are consistent with an asphyxiation agent and of a nerve agent of some type,"Reuters reported.

US President Donald Trump tweeted on Sunday that al-Assad will have a "big price to pay" for the alleged attack.

Chlorine gas is a powerful irritant that can wreak havoc on the human body, but isn't known for being extremely lethal. However, it does sink and displace breathable air, so it can asphyxiate people in underground environments.

Just a small amount of sarin gas, however, can be extremely deadly.

Here's what sarin gas is and what it does to the body, according to information from the Centers for Disease Control and Prevention, Reuters, and other sources.

Where the toxin comes from and what it is

Sarin is a nerve agent that:

• Was developed in Germany in 1938 as a pesticide.
• Is a human-made substance that's similar to insecticides called organophosphates, yet is far more powerful.
• Is clear, colorless, tasteless, and odorless liquid in pure form, and dissolves easily in water.
• Rapidly evaporates into a dense gas that sinks to low-lying areas, and is the most volatile of all nerve agents.
• In a bomb, mixes as two chemicals to weaponize the nerve agent.
• Can affect people through their skin, eyes, and lungs, and through contaminated food and clothes.
• Was used in attacks on Japan in 1994 and 1995.
• Was used by Bashar Assad's regime during an attack in Syria in 2013.

Why nerve agents are so deadly

The two following illustrations explain how most nerve agents like sarin affect the body.

To produce these symptoms, nerve agents attack the body's cholinergic system, which is used to transmit signals between the brain and muscle tissues.

The chemicals specifically target an enzyme that drifts in the spaces, or synapses, between nerve cells and muscle cells. There, they persist and constantly trigger muscles into overdrive.

This can paralyze victims, stop their breathing, and trigger convulsions, all of which can lead to death.

This story has been updated. It was originally published at 12:02 a.m. EDT on April 10, 2018.

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• The Russian ruble is down 4.1% against the dollar on Tuesday morning.
• It follows a slide of more than 4% on Monday after the US imposed sanctions late on Friday night.
• Analysts say there is a "high" risk tensions between the US and Russia escalating further.

LONDON — The Russian ruble is falling against the dollar on Tuesday as the currency continues to reel from US sanctions imposed by the Trump administration.

The ruble is down 4.1% against the dollar at 2.20 p.m. GMT (9.20 a.m. ET). It follows a fall of more than 4% against the dollar on Monday after the Trump administration on Friday imposed new sanctions on 24 wealthy Russians and government officials, as well as over a dozen Russian-controlled entities.

Hussein Sayed, the chief market strategist at FXTM, said in an email on Tuesday morning: "The new geopolitical risks over the increased conflict in Syria cannot be ignored. This came after the U.S. imposed a wide range of financial sanctions on Russian assets, causing stocks to suffer their worst performance in four years and the ruble falling as much as 4.1%.

"Russia warned the U.S. that any military reprisal to Saturdays’ chemical attack in Syria could have 'grave repercussions'. Will U.S. and Russia go into a confrontation in Syria? This likely depends on Trump’s decision over the next 24 hours, but the risks are high."

Michael Hewson, the chief market analyst at CMC Markets UK, noted in an email that John Bolton started as President Trump's new national security advisor on Monday, potentially raising the likelihood of confrontation between the US and Russia.

"Coming on the back of events in Salisbury last month and the use of a nerve agent there, and the fact that renowned Russia hawk John Bolton started his role as National Security Advisor in the White House yesterday, the risk is that last weekend’s measures may only be the start to financially ostracize Russia," Hewson said.

Ivan Glasenberg, the CEO of London-listed commodities trader Glencore, on Tuesday resigned from the board of Russian aluminum producer Rusal in response to the US sanctions. The company's stock fell 8.9% in response.

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