Russia is taking a more active role in propping up the regime of Syrian President Bashar Assad, expanding its physical footprint in the Middle East.
American officials admitted to The New York Times that Russia is now using an air corridor over Iran and Iraq to transport military equipment and personnel to Syria despite US attempts to guard this airspace.
And Russian advisors have taken over the main airport near the capital, positioning tanks and directing flights.
Russia is reportedly transporting marines, pre-fabricated housing for at least 1,000 people, a portable air traffic control system, and other items that could be used to create an air base for air combat operations to northwest Syria, according to CBS News.
This constitutes "the most significant new Russian military foothold in the Middle East in decades," American officials told the Times. Continued Russian military buildup in Syria could "greatly enhance [Russia's] ability to project power in Syria and neighboring states," according to the Times.
"This is the most important Russian power projection in the region in decades and it will enhance Russia’s influence throughout the Levant," Stephen Blank, a Russian military expert at the American Foreign Policy Council, told the Times.
Michael Morell, the former deputy director of the CIA, told CBS News last week that flying over Iran and Iraq was Russia's last viable option for transporting the material and personnel to Russia after Turkey and Bulgaria refused to let Russia use its airspace for flights to Syria.
Iran has already agreed to let Russia run flights over the country, which leaves it up to Iraq to decide whether to stop the flights. The US has objected to the Syria flights, but Russian foreign minister Sergey Lavrov said they would continue, according to the Times.
"There's only one thing we can really do, which is try to stop the flow of these arms [to Syria]," Morell said. "... I think the diplomatic focus is now going to be on Iraq and the US is going to put tremendous pressure on Iraq to stop those flights."
But this might not be easy for Iraq to do.
"Neutrality is the best Washington can hope for in Baghdad," Ramzy Mardini, a nonresident fellow at the Atlantic Council, told the Times. "Iraq is not a dictatorial state like many of the U.S. allies in the Middle East.
"Iraq is still a fragile state whose leaders are exposed to politics. In the discourse of Iraqi politics, forcing Abadi to side with the US against Assad is like realigning him with the Sunni axis against the Shia one."
Russia, one of Assad's primary backers along with Iran, had initially said that it was only sending "military experts" to Syria to help government forces learn how to use Russian military equipment. But the Israeli defense minister and Reuters have since confirmed that the Russians are taking part in the fighting on behalf of Assad and building up their military presence in the western coastal province of Latakia.
The increased support from Russia comes as Assad is doing everything he can to hold onto power amid a bitter civil war that has created a massive refugee crisis as millions of Syrians flee their country. Assad has dropped steel barrels full of shrapnel and explosives on civilian areas and used chemical weapons against Syrians in an effort to retain his control over key territories.
Natasha Bertrand contributed to this report.
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