WASHINGTON, June 26 (Xinhua) -- U.S. Acting Secretary of Defense Mark Esper reiterated U.S. disapproval of Turkey purchasing Russia's S-400 air defense system, while meeting with his Turkish counterpart Hulusi Akar, the Pentagon said Wednesday.
Esper and Akar had "a frank and transparent discussion" about the issue on the sidelines of a meeting of the North Atlantic Treaty Organization (NATO) defense ministers in Brussels on Wednesday, Pentagon chief spokesperson Jonathan Hoffman said in a statement.
Esper noted that Turkey's purchase of the Russian S-400 air and missile defense system is incompatible with the F-35 program and that Turkey will not be permitted to have both systems, according to the statement.
The United States and its NATO ally Turkey have been sparring for months over the latter's purchase of the S-400, which Washington argued could gain valuable intelligence on the technical systems of the U.S.-made stealth F-35 jets when the S-400 is deployed on the Turkish territory.
Washington is reportedly halting the training of Turkish pilots of U.S. F-35 fighter jets in addition to threatening economic and other military sanctions as Ankara insists on its S-400 deal with Russia.
Turkish President Recep Tayyip Erdogan said earlier this month that he would discuss the issue with his U.S. counterpart Donald Trump during the upcoming G20 summit in Japan.
Erdogan also threatened that Turkey would retaliate if the United States imposes sanctions over its purchase of the Russian S-400 air defense system.