The United States has voiced concern over Turkey's purchase of S-400 air defense systems, urging Ankara to abandon its agreement with Moscow, "eliminating any risk that could harm NATO allies," although the military bloc previously indicated that the acquisition is Turkey's national decision.

"We are very concerned about any kind of Russian missile defense in one of our alliance countries," U.S. Ambassador to NATO Kay Bailey Hutchison told reporters in an interview Tuesday, ahead of a NATO defense ministers meeting. If Turkey does purchase Russian arms, it could put at risk the types of defenses other NATO allies could have in the country, affect the interoperability of defense systems and violate security and intelligence among alliance members, Hutchison noted. Regardless of continuous warnings from the U.S., NATO Secretary-General Jens Stoltenberg last April described Turkey's plan to purchase S-400 air defense missile system as a matter of "national decision."

Ankara opposes any prerequisite in the contract that foresees the cancellation of the S-400 defense systems. President Recep Tayyip Erdoğan also previously said that S-400 missile system negotiations between Ankara and Moscow are a done deal, and the U.S. was not in a position to say something about it, adding that Turkey needs both Russian-made S-400 air defense systems and U.S.-made F-35 fighter jets.

On Dec. 19, 2018, the U.S. State Department approved a possible sale of the Patriot air and missile defense system, saying that Turkey continues to be an essential element of the national security and defense strategy. This was regarded as a breakthrough move after Washington's delay of F-35 airplanes to Turkey due to its purchase of the Russian-made S-400 defense system.

On the sidelines of the NATO meeting, Defense Minister Hulusi Akar met with Patrick Shanahan, the acting U.S. defense secretary, yesterday to discuss a number of issues, including Turkey's purchase of S-400 systems.