An unnamed US diplomat on May 21 said: "Turkey will face serious consequences if the S-400 anti-aircraft missile system is completed. They have 2 weeks to decided to choose US weapons or take sanctions for buying Russian missiles ".

Observers said Turkey could completely be disqualified from the US F-35 stealth fighter program, not to hand over the ordered F-35A fighter and be subject to multiple orders. embargo from Washington. To avoid this scenario, Ankara had only one option to cancel the purchase of the S-400 missile system and select the American-made Patriot system.

According to US diplomatic officials, the deadline for Turkey will not be delayed further. NATO member countries need to buy weapons capable of synergizing with each other. While Russian weapons cannot meet that standard. In addition, Washington also pledged to accelerate the delivery of Patriot air defense systems if Ankara abandoned the Russian S-400.

Earlier, the Turkish President announced on May 18: "There is no doubt that Turkey will buy Russia’s S-400 anti-aircraft missile system. After that, the two sides will cooperate. Production of S-500 air defense systems ".

Reportedly, Russia is expected to hand over to the first S-400 system in July.