ANKARA, March 10. /TASS/. The United States has requested Turkey to guarantee that the S-400 anti-aircraft missile systems purchased from Russia will not come into operation, Turkey’s President Recep Tayyip Erdogan told Turkish journalists aboard his airliner upon flight from Belgium to Turkey, the CNN Turk television channel reported on Tuesday.

"As you know, we have made a proposal to the United States on the issue of Patriot air defense systems: if you are going to give us Patriot launchers, let us buy them. But as for the S-400s, they have also quite softened their stance. Now they are requesting us to promise that we will not put S-400s into operation," the Turkish president said.

The Turkish president said on March 6, however, that Turkey would start deploying S-400 anti-aircraft missile systems in April.

Russia announced in September 2017 that it had signed a $2.5 billion deal with Turkey on the delivery of S-400 anti-aircraft missile systems to Ankara. Under the contract, Ankara will get a regiment set of S-400 air defense missile systems (two battalions). The deal also envisages partial transfer of production technology to the Turkish side.

Turkey is the first NATO member state to purchase such air defense missile systems from Russia. The deliveries of S-400 launchers to Turkey began on July 12, 2019.

The United States and NATO have been making attempts to prevent Turkey from purchasing Russia's S-400 missile systems. Washington has warned on many occasions that it may impose sanctions on Turkey, if Ankara presses ahead with the S-400 deal. On July 17, 2019, the press secretary of the US White House said in a written statement that Turkey’s decision to acquire Russian-made S-400 air defense systems rendered Ankara’s further participation in the US program of the fifth-generation F-35 fighter-bomber impossible.

The S-400 ‘Triumf’ is the most advanced long-range air defense missile system that went into service in Russia in 2007. It is designed to destroy aircraft, cruise and ballistic missiles, including medium-range weapons, and can also be used against ground installations. The S-400 can engage targets at a distance of 400 km and at an altitude of up to 30 km.