The Pentagon announced on Friday that if Turkey did not give up on the S-400 system by July 3, Ankara would be blocked from purchasing F-35 fighter jets and Turkish pilots now training in the U.S. would be expelled.
Turkey's President Erdogan says he hopes a Russian missile system that Washington sees as a threat to U.S. jets will be delivered in July. He did add that he was speaking to his Turkish counterpart and they were "making progress on discussions" about the S-400.
He said: "Turkey won't reverse its decision with such letters". The U.S. and Turkey's North Atlantic Treaty Organisation allies have consistently argued that the system is incompatible with North Atlantic Treaty Organisation weapons systems.
During Wednesday's meeting, Erdogan said Turkey will "hold to account" anyone who excludes Turkey from the F-35 programme "due to reasons without reason or legitimacy".
But in the following days, Shanahan told reporters he was unaware of the Turkish request to form a working group.
Shanahan said on Friday the U.S. offer for the Patriots was "very competitive" but Erdogan said Russian Federation offered a better deal including reasonable pricing and a joint-production promise.
Turkey on Wednesday criticised a letter from Washington on Ankara's eventual removal from the F-35 fighter jet programme, saying the language used did not suit the spirit of alliance between the two North Atlantic Treaty Organisation allies.
"This is not an attack system but a defense system".
Erdogan is scheduled to meet with President Donald Trump on the margins of Group of 20 (G20) summit in Japan on June 28-29, but the Turkish leader said he will speak to the USA president by phone on June 13. "The necessary initiatives have been undertaken with Russian Federation in connection with the attack", it said. Ankara has proposed that the two allies form a working group to assess the impact but says it has yet to hear back from Washington.
Patrick Shanahan sent a letter to Hulusi Akar last week, seen by the Foreign Policy magazine, in which he said Turkish trainees would have to leave the United States by July 31.
Erdogan also said he wanted to talk about the issue on the phone with the United States, before he meets President Donald Trump in Osaka, Japan at the end of this month.
"We have so far paid $1.250bn", he said.
Russian Federation said on Tuesday it planned to deliver its S-400s to Turkey in July, setting the clock ticking on the USA sanctions threat.