"Do not forget that Turkey is a NATO country. America is a NATO country. I am not aware if NATO countries place sanctions on one another," Erdogan told reporters at an Ankara airport, before leaving for Japan where he will attend the G20 summit.

Erdogan is due to meet Saturday with US President Donald Trump on the margins of the summit in Osaka. Turkey's deal with Russia will be one of the issues on the table.

The US has given Turkey a deadline of July 31 to drop the purchase of the S-400 system, or face sanctions and removal from the United States' F-35 fighter jet programme.

Erdogan is hoping to use good relations with Trump in order to defuse tensions when they meet this weekend.

He said Turkey's relations with Washington was based upon "strategic partnership" and added he did "not get such an impression from Mr Trump" that sanctions would be placed unless Ankara dropped the Russia deal.

The Turkish leader also insisted that the agreement with Moscow was a "done deal" and that the system was "in the process of delivery."

Erdogan this week said his country would take delivery of Russia's S-400 missile defence system in July.