Russian servicemen drive S-400 missile air defence systems during the Victory Day parade, marking the 73rd anniversary of the victory over Nazi Germany in World War Two, at Red Square in Moscow, Russia May 9, 2018. REUTERS/Sergei Karpukhin/File Photo

MOSCOW (Reuters) - The Kremlin said on Wednesday Russia was pressing ahead with a contract to deliver advanced S-400 missile air defense systems to Turkey despite the U.S. State Department approving the possible sale of a rival U.S. missile defense system to Ankara.

The Pentagon said on Tuesday that the U.S. State Department had approved a possible $3.5 billion sale of Patriot air and missile defense systems to NATO-ally Turkey, after notifying Congress of the certification.

Russia and Turkey have already concluded a deal for Ankara to buy the rival Russian S-400 system with deliveries expected to begin next year despite the United States and NATO member countries, already wary of Russia’s presence in the Middle East, warning it is not compatible with NATO defenses.

Speaking to reporters on a conference call, Kremlin spokesman Dmitry Peskov said that the Russian and U.S. transactions should be seen as separate from each other, and that Russia was in the process of fulfilling the terms of the deal to supply Ankara with S-400s.

“These are not connected processes. In this case, we are fulfilling agreements that we have with our Turkish colleagues. You know that the contract is being fulfilled. This will be continued,” Peskov said.

He said that Russia trusted Turkey not to disclose secrets about the S-400 system to its NATO partners.

“We don’t see any grounds not to trust our Turkish colleagues,” Peskov said, when asked if Moscow had concerns Ankara might share sensitive data about the S-400s with the Americans.

U.S. and NATO officials have repeatedly warned Ankara that the Russian system cannot be integrated into the NATO air and missile defense system and that purchasing the S-400 system would jeopardize Turkey’s purchase of Lockheed Martin Corp F-35 fighter jets and possibly result in Washington imposing sanctions.

Turkey said last month that its purchase of the Russian missiles was a done deal and could not be canceled. It said it needed to buy further defense hardware however, which could be bought from the United States.