The US and Turkey have clashed over the latter's purchase of Russia's S-400 missile-defense system.

Turkey's president says the sale will go ahead and that Ankara may even buy the next version of the system.

ANKARA (Reuters) - Turkey will never turn back from a deal to purchase S-400 missile defense systems from Russia, President Tayyip Erdogan said on Wednesday, adding that Ankara may subsequently look into buying S-500 systems.

Washington has previously warned that procuring the S-400 systems from Russia could jeopardize defense industry deals between the NATO allies, and this week decided to end preferential trade with Turkey.

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In an interview with broadcaster Kanal 24, Erdogan also said that the United States should not try to discipline Turkey though trade measures, adding that Turkey had its own measures prepared.

Washington has previously warned that procuring the S-400 systems from Russia could jeopardize defense industry deals between the NATO allies, and earlier this week decided to end preferential trade with Turkey.

(Reporting by Tuvan Gumrukcu)