Turkey received its first shipment of S-400s in July, prompting Washington to suspend it from the F-35 fighter jet programme, halt its order of 100 of the new-generation jets, and begin procedures to sanction the country under the Countering America's Adversaries Through Sanctions Act (CAATSA), designed to discourage countries from arms deals with Russia.

“We continue to stress at the highest levels that the S-400 transaction is the subject of ongoing CAATSA sanctions deliberations and it remains a major obstacle in the bilateral relationship and at NATO," Ortagus said in an email to Reuters.

Turkey had previously said it would make the Russian missile defense systems operational in April.

The missile showdown between Turkey and the United States appeared to be put on hold due to the coronavirus pandemic as Turkey focused efforts on combatting the pandemic.

But a senior Turkish official on Monday said Ankara had no intentions to reverse its decision and that activation of missiles systems had only been delayed.

Reporter’s code: 50101