MOSCOW

Russian presidential spokesman on Wednesday rejected what he called "U.S. ultimatums" to impose sanctions on Turkey if Ankara moves ahead with the delivery of Russian-made S-400 air-defense systems.

"We take ultimatums extremely negatively, we consider such ultimatums unacceptable," Dmitry Peskov told reporters in Moscow.

Peskov said the Turkish leadership has made "numerous statements" that the deal on the S-400 is already completed.

"Now it is being implemented," he said.

On Tuesday, the Turkish defense minister has said Turkish military personnel are currently receiving training in Russia for the use of the S-400 air defense system.

"We’ve sent personnel to Russia for S-400 training that will begin in the coming days and will span the following months," Hulusi Akar told reporters.

Tensions between the U.S. and Turkey have reached a fever pitch in recent months with Turkey set to begin receiving the advanced S-400 surface-to-air missile system.

U.S. officials have said Turkey should buy the U.S. Patriot missile system rather than the S-400, arguing it is incompatible with NATO systems and is a threat to the F-35 fifth-generation stealth aircraft.

Turkey responded it was the U.S. refusal to sell it Patriots that led it to seek other sellers, adding that Russia offered a better deal, including technology transfers.

The U.S. officials have suggested that Turkey might be removed from Lockheed Martin's F-35 program and lose 100 promised F-35 warplanes and face other sanctions.