The United States continues to consider the S-400 air defense system a threat to its F-35 fifth generation stealth fighter platform, and may impose sanctions against Ankara, Turkey's Anadolu news agency has reported, citing a high-ranking source in Washington.
"I can't say for certain whether sanctions will be imposed on Ankara over the S-400 contract, but the possibility is there. The US administration is not optimistic about this issue," the source said.
The source also characterised the deployment of S-400s in areas where US F-35 fifth-generation stealth fighters are set to fly as "a threat," without elaborating.
Emphasizing that negotiations between Washington and Ankara on the issue were "continuing," the source said that there were also "positive tendencies" in negotiations between the two countries on the procurement of the Patriot system, Washington's closest analogue to the S-400 in terms of capabilities.
Washington has already slapped China with sanctions over its purchase of S-400s and Su-35 combat aircraft in September. India, however, has voiced confidence that it would not be hit with similar restrictions, which the US Treasury has pursued under the 2017 Counter America's Adversaries Through Sanctions Act (CAATSA).