© Reuters/Sergei Karpukhin
Moscow has said that Washington's decision to set a deadline for Turkey to pull out of the S400-deal with Russia is an "unacceptable" ultimatum.

On Tuesday, reports in the US media suggested that the White House was urging Ankara to abandon the deal to purchase the S-400 air defense system by the end of the first week of June, or it would face consequences including sanctions.

"We have a negative view of ultimatums in general, we consider them unacceptable," Kremlin spokesperson Dmitry Peskov said, calling the S-400 agreement with Turkey a done deal.

As a NATO-state, Ankara has been trying to buy four batteries of the Russian S-400 systems, the first of which should arrive in July, despite the strong opposition from the US. Washington wants Turkey to purchase American defence systems, arguing that the S-400 is not compatible with NATO systems and also citing security concerns over Russian equipment working alongside their own.

The US fears that Turkey's deal with Russia would compromise the security of the F-35, threatening to kick Turkey out of participation in the program and cancel its order for the jets.