After the situation calmed briefly, the US Treasury Secretary Stephen Mnuchin on Monday, September 9th, has repeated talk of possible Washington sanctions on Ankara over the Russian S-400 missile deal.
Mnuchin said that President Trump's administration was considering sanctions against Turkey's purchase of the Russian-made S-400 air defence system, but no decisions were made.
"We're looking at it. I'm not going to make any statements about any specific decisions, but we're looking at it," Mnuchin told reporters outside the White House when asked if the Treasury Department was considering sanctions. He did not specify any possible sanctions targets.
As a result, Turkey's dollar-denominated sovereign bonds fell after Mnuchin's comments, Turkish news portal, Ahval, said.
Ankara and Washington are at odds over Turkey's purchase of the S-400, which the United States says is incompatible with NATO defences and poses a threat to Lockheed Martin's stealth fighters.
Russia handed Turkey a second S-400 battery last month, Interfax news agency quoted Russian President Putin as saying. Ankara received the first shipment in July.
Washington has already warned Turkey that it would face sanctions over the purchase of the system and excluded Ankara from the F-35 programme, but Turkey still rejects the warnings.
The dispute over the air defence system is among several issues that have strained relations between the United States and Turkey, including the conflict in Syria.
Patrick Shanahan, who was acting defence minister, had already sent a letter to Ankara until July 31st to stop buying S-400 missiles.
However, Turkish President Recep Tayyip Erdogan is counting on his relationship with Trump to avoid sanctions.
In this context, Erdogan said that Trump has the power to refrain from imposing sanctions on Turkey, for buying Russian air defence systems, and he must find a "compromise" in this dispute.
Trump expressed sympathy for the Turkish position during his meeting with Erdogan during the G20 summit in Japan, saying that Ankara had to buy the S-400 system from Moscow because the former US administration refused to sell Patriot missiles.
Republican and Democratic lawmakers have called for the cancellation of Ankara's handover of F-35 fighter jets, and have demanded sanctions against Turkish officials involved in the deal with Russia.
"President Erdogan has given us the choice, and he has clearly made the wrong choice," Eliott Engel and Michael McFaul, the two leading Democrats and Republicans on the House Foreign Affairs Committee, said in a joint statement.