Russian S-400 missile air defence systems on display during a parade at Red Square in Moscow, May 9, 2018. (REUTERS)

MOSCOW, April 14 (Xinhua) -- Kremlin Spokesman Dmitry Peskov on Sunday spoke highly of Turkey's tough stance on the purchase of Russian S-400 air defense missiles despite U.S. opposition.

Calling the U.S. pressure on Ankara "unprecedented," Peskov told a Russian TV program that Moscow welcomes the position of Turkish President Recep Tayyip Erdogan, which allows the two countries to build "free and sovereign dialogue."

Washington has criticized Turkey's purchasing of Russian S-400 missiles and the Pentagon said last week that it had halted deliveries of F-35 fighter jet parts and manuals to Turkey.

Nevertheless, Erdogan and Russian President Vladimir Putin on Monday agreed to implement their contract and deliver the S-400s to Turkey as planned.

The S-400 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.