The U.S. government will end the process of the Patriot sale if Turkey proceeds with the purchase of the Russian S-400 air defense systems, a senior U.S. official has told Hürriyet Daily News.

“We will not proceed as the condition of the congressional authorization to make the offer to Turkey, we’re not in a condition to proceed with the Patriot sale if the S-400 sale goes forward, “said the official on condition of anonymity.

“We are very concerned that the Turkish purchase of S-400 missiles will endanger Turkish participation in the F-35 program and will likely result through our legislation in some sort of sanctions coming through the legislations called CAATSA,” the official stated, elaborating on recent talks between Ankara and Washington at which the latter brought forward a proposal for the procurement of the Patriots.

The U.S. has formally made an offer to Turkey for the sale of the multibillion dollar Patriot air defense systems in January in a bid to increase its pressure on the latter’s purchase of the Russian-made S-400 systems. But Turkey says it would buy Patriot systems from the U.S. but not on the condition of cancelling the S-400 systems from Russia.