The United States wants NATO allies to have the interoperable equipment, and Turkey would need to explain for itself the choice of the Russian S-400 air defence systems, US Department of Defense spokesperson Capt. Jeff Davis said in a briefing on Monday.
"Turkey is a NATO ally, and one of the cornerstone things that we like to have with any of our allies...is the ability to have equipment that interoperates," Sputnik cited Davis as saying.
"The reports of the S-400, and Turkey's purchase of that, Turkey would need to explain that for itself," he added.
