Washington is alarmed about the S-400 surface-to-air missiles (SAMs) deal between Moscow and Ankara, US Permanent Ambassador to NATO Kay Bailey Hutchison told a news briefing on Tuesday.
"We are very much concerned about any supply of Russian missile defence systems to any of our allies. We urge Turkey not to continue the development of this deal because it will not allow us to deliver the defence systems to Turkey which we could install there," Hutchison pointed out.
She stressed that "in any case the S-400 systems would not be compatible" with air defences of the United States and its allies.
"This is very disturbing and all our allies are concerned about this. We all hope that Turkey will make the right decision," Hutchison concluded.
Her remarks came a few days after Turkey's Hurriyet Daily News cited an unnamed senior US official as saying that Washington would halt the sale of Patriot batteries to Ankara if the country proceeded with the purchase of Russian-made S-400 air defence systems.
The official also expressed alarm that "the Turkish purchase of the S-400 systems will endanger Turkish participation in the F-35 programme and will likely result through our legislation in some sort of sanctions coming through the legislations called CAATSA".
The US official's comments followed a statement by Turkish presidential spokesman Ibrahim Kalin, who warned that the Patriot deliveries should not be linked to the S-400 deal.
"Our position remains unchanged: we will do everything that we deem necessary to ensure our national security. […] Turkey may buy Patriot systems in the future. But it will be impossible if abandoning the S-400 is one of the conditions for the purchase," he stressed.
Turkey and Russia finalised a contract on the sale of four S-400s batteries in December 2017, with the first of these systems expected to be delivered later this year.