MOSCOW, July 9 (Xinhua) -- Russian-made S-400 air defense missile systems are being delivered to Turkey according to existing plans, Kremlin spokesman Dmitry Peskov said Tuesday.

"The deliveries are taking place on time under the existing contract," Peskov was quoted by Tass news agency as saying, in response to questions about the schedule of the first deliveries.

On Thursday, head of Turkish Defense Industries Ismail Demir said that the delivery of Russia's S-400 systems would start in the second week of July. The Turkish TV channel Heberturk reported Friday that the first S-400 missile system could be delivered to Turkey on Tuesday.

In 2017, Russia and Turkey finalized a deal to supply Ankara with two batches of S-400 surface-to-air missile batteries. In April 2018, both parties agreed on early delivery of the systems.

According to the Turkish Defense Ministry, the deployment of S-400 missile systems is likely to begin in October.

The United States warned previously that it might deny Turkey the purchase of F-35 fighter-bombers if the latter proceeds with the S-400 deal.

The S-400 air defense missile system is considered the most advanced of its kind in Russia, capable of destroying targets at a distance of up to 400 km and a height of up to 30 km.