Turkey announced earlier this week that it had finalized a multibillion-dollar purchase of the S-400, Russia's most sophisticated surface-to-air-missile system.
The acquisition has been discussed for several months and comes amid a period of strained relations between Ankara and its partners in the NATO military alliance.
Finalizing the $2.5 billion deal appears to have inflamed those tensions however, and at least one US senator is saying sanctions on Turkey may now be necessary.
Turkey's purchase of the weapons system appears to stem in part from reluctance by NATO members to sell it certain arms. Turkish President Recep Tayyip Erdogan has criticized the alliance several times since announcing the purchase on Tuesday.
"Nobody has the right to discuss the Turkish republic’s independence principles or independent decisions about its defense industry," Erdogan said on Tuesday. "We make the decisions about our own independence ourselves — we are obliged to take safety and security measures in order to defend our country."
He was more direct the following day, saying NATO "went crazy just because we made the S-400 deal. What were we supposed to do? Wait for you? We are taking care of ourselves. We are taking security measures and will continue to do so."
NATO has warned Turkey that members of the alliance are obligated to use military hardware that is interoperable with each other's systems. (NATO leaders are also wary of the introduction of Russian equipment to a NATO member's military.) Turkey, for its part, has rebutted that by citing Greece's purchase of Russia's S-300 missile system several years ago.
Turkey has also criticized the US and its allies for their reticence about selling it military arms and technology. Ankara has touted the technology transfer component of the deal with Russia, which will aid its rapidly expanding domestic defense industry.
A NATO spokesperson told Politico that the bloc had not been informed about the details of the purchase. However, they said, "It is up to allies to decide what military equipment they buy."
Maryland Sen. Ben Cardin, the ranking Democrat on the Senate Foreign Relations Committee, was less sanguine about the deal, asking the Trump administration to review its impact on US-Turkey security cooperation and on Turkey's NATO membership.
In a letter to Secretary of State Rex Tillerson and Treasury Secretary Steve Mnuchin, Cardin warned that the deal violated a bill signed into law in August that imposes sanctions "on any person that conducts a significant transaction with the Russian Federation’s defense or intelligence sectors."
"These are mandatory sanctions and constitute a commitment by the United States to deter Russia from attacking the United States and its allies in the future," the letter said, according to Politico.
The White House has resisted the sanctions measure as interference in the president's freedom to conduct diplomacy, and the State Department has stopped short of discussing punishment in this case. But the Pentagon has expressed more worry about the acquisition.
"We have relayed our concerns to Turkish officials regarding the potential purchase of the S-400. A NATO interoperable missile defense system remains the best option to defend Turkey from the full range of threats in its region," Pentagon spokesman Johnny Michael said in a statement.
The deal also carries diplomatic weight.
The Erdogan government was irritated by what it saw as an lackluster response to an attempted coup against him in summer 2016. Germany has been a particular target of ire, especially after Berlin decided to limit some arms sales to Turkey over concerns about a crackdown and mass arrests in the wake of that coup.
In addition to frustration about arms sales, Turkey has been dismayed with the US's cooperation with the YPG, a mostly Kurdish group fighting ISIS in Syria. Turkey considers the group an offshoot of the Kurdish rebel group PKK, which both Ankara and Washington have labeled a terrorist group.
The deal also underscores what many in the West see as an increasingly cozy relationship between Russia and Turkey. Some view the sale as another step by Moscow to undermine NATO — a sentiment Russian presidential adviser Vladimir Kozhin may have tried to nurture by saying, "I can only guarantee that all decisions taken on this contract strictly comply with our strategic interests."
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