Turkish President Tayyip Erdogan stated that Turkey will produce S-500 anti-aircraft missile systems in cooperation with Russia, Reuters reported.

The United States, a military ally in the NATO alliance, has threatened sanctions against any country that purchases Russian defense systems. Turkish-US relations became strained after Turkey pushed forward with the purchase of Russia’s S-400 missile defense system.

 “There is absolutely no question of (Turkey) taking a step back from the S-400s purchase. That is a done deal,” Erdogan said.

 According to Turkish newspaper Haberturk, Erdogan reported that Turkey had sent 100 engineers to Russia to help make the weapons.

 In early May, Rostec CEO Sergey Chemezov stated that Russia values the development of technologic partnership with Turkey in air defense.

 “We will welcome the Turkish side’s wish to become a partner in the S-500 project,” he noted.

Earlier this year, US officials told Turkey to scrap its deal to acquire the S-400, saying it would not be compatible with its current arsenal of American military hardware.

 Washington also voiced concerns that the S-400 would compromise its F-35 fighter jets, saying Turkey’s plan to buy into the Russian-built system is “deeply problematic.”

 Last month, the US halted deliveries of F-35 related equipment over Turkey’s refusal to back down from the S-400 deal with Russia.

 The US is “passing the ball around in the midfield now, showing some reluctance,” Erdogan said on Saturday.

 “But sooner or later, we will receive the F-35s. The US not delivering them is not an option,” he added.