"Our position has not changed," Pentagon spokesman John Kirby told reporters. "We urge Turkey not to retain the S-400 system."

Turkey turned to Russia after failing to agree terms with Barack Obama's administration about the purchase of US Patriots -- the air defense system of choice for most NATO member states.

It took delivery of the $2.5 billion S-400 system in defiance of warnings that such military cooperation was incompatible with NATO and would let Russia improve its targeting of Western planes.

In retaliation, Washington banned all US export licenses and loan credits for Turkey's military procurement agency, the Presidency of Defense Industries.

Earlier it had also evicted Turkey from joint efforts in developing the F-35 fighter-jet.

"Turkey is a longstanding and valued NATO ally, but their decision to purchase the S-400 is inconsistent with Turkey's commitments as a US and NATO ally," Kirby continued during a press briefing.

"Turkey had multiple opportunities over the last decade to purchase the Patriot defense system from the United States and instead chose to purchase the S-400, which provides Russia revenue, access and influence," he noted.

Turkish President Recep Tayyip Erdogan had expressed the hope in January of reaching a compromise with Biden that would allow Ankara to be reintegrated into the F-35 fighter aircraft program, but contacts between the new American administration and Turkey have been limited.

While Ankara said on Tuesday that Turkish presidential spokesman Ibrahim Kalin and US national security advisor Jake Sullivan had expressed wishes for greater cooperation, on Friday Biden still had not yet spoken with Erdogan since becoming president.