US Treasury Secretary Steven Mnuchin
US Treasury Secretary Steven MnuchinReuters

US Treasury Secretary Steven Mnuchin said on Monday that the Trump administration was considering imposing sanctions over Turkey’s purchase of the Russian-made S-400 air defense missile system, though he said that no decisions have been made.

“We’re looking at that, I’m not going to make any comments on any specific decisions, but we are looking at it,” Mnuchin told reporters outside the White House, according to Reuters.

He did not specify any potential targets.

Ankara and Washington have been at loggerheads over Turkey’s purchase of the S-400 system, which the United States says is not compatible with NATO defenses and poses a threat to Lockheed Martin’s F-35 “stealth” fighter jet.

The first parts of the S-400 air defense system were delivered to Turkey in July. Russia then delivered a second battery of S-400s last month.

Washington reacted to Turkey's purchase of the S-400 by removing the country off its F-35 fighter jet program.

Turkish officials insist that the deal to purchase the S-400 does not affect the security of the US and have repeatedly stressed that they will go ahead with the deal despite Washington’s objections.

Turkish President Recep Tayyip Erdogan said after the delivery of the first parts of the system that Turkey planned to start using the S-400 in April of 2020.