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 told Russian news agency TASS in response to questions about the schedule of the first deliveries. 

The head of Turkish Defense Industries Ismail Demir said Thursday 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. 

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

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

The United States warned 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.

(Cover: People walk past Russian S-400 missile air defense systems before the military parade to commemorate the 75th anniversary of the battle of Stalingrad in World War Two, in Volgograd, Russia, February 2, 2018. /Reuters Photo)