In what was Turkey's first response to the letter, Cavusoglu said no one can give Turkey ultimatums. The move would also see Turkey locked out of receiving the next generation of F-35 stealth fighter jets from the US. President Tayyip Erdogan had said on Wednesday. that Turkey had already purchased the S-400 defence systems and hoped they will be delivered in July.
Speaking at a meeting of his AK Party members, Erdogan said Turkey will hold to account anyone who excludes Turkey from the F-35 program.
Mr Erdogan said he hoped to resolve the situation with the U.S. through phone diplomacy ahead of a meeting with President Trump at the end of June, Reuters reported.
"Turkey has already bought S-400 defence systems".
Erdogan has resisted US pressure to back out of the Russian purchase, saying it is a done deal and has dismissed suggestions it is a threat to North Atlantic Treaty Organisation systems.
"However, unfortunately, the U.S. side has not given us an offer as good as the S-400s", he said.
Turkey hopes that Trump and Erdogan's personal rapport can help it skirt sanctions Congress plans to implement over the S-400s, even though the American leader lacks the authority to veto the measures created to dissuade countries from doing business with Russian defense and intelligence entities.
Turkey has repeatedly proposed a joint working group to assess the impact of the S-400 surface-to-air defense systems, but Washington has not yet taken up the suggestion.
"We are not going to request anyone's approval to satisfy our needs regarding the defense industry".
"This is not an attack system but a defense system".
Turkey and the United States have sparred publicly for months over Ankara's order for the S-400s, which the U.S. says are incompatible with NATO's defence network and pose a threat to US F-35 fighter jets that Turkey also plans to buy. Yes, we did. Did they deliver?
They did not say how long the ceasefire would last.
As well as these immediate responses, the S-400 deal threatens to undermine Turkey's role in North Atlantic Treaty Organisation - a cornerstone of its security policy since it joined in 1952. "The presidents of Turkey and the United States will discuss the issue of our F-35 trainees at a meeting on the sidelines of the G20 summit in Japan on June 29", Kalin told reporters.
The US has also threatened to hit Turkey with sanctions if it goes ahead with the deal.