The governor's office in Ankara said on Sunday that military planes, including F-16 fighter jets, would circle the capital on Monday and Tuesday as part of "anti-air defence system tests", without specifying the system.

Pro-government newspaper Milliyet confirmed Monday that it was the S-400 system, bought from Russia earlier this year to the consternation of Turkey's NATO allies.

The purchase has raised particular tensions with the US, which argues there is a risk that sensitive technological information could be leaked if the S-400 is used alongside Western systems such as the new F-35 jet.

Turkey has ordered 100 F-35s and its defence industry was part of the supply chain for the new jet, until it was kicked off the programme after the S-400 purchase was finalised in July.

So far, the US has appeared reluctant to impose threatened sanctions on Turkey over the purchase, with officials saying it could be spared if it does not activate the S-400 system -- though this option has been rejected by Turkey.