Turkey’s purchase of the Russian defense system S-400 is not a technical problem but a political one, a German expert said on Monday. “It's a political problem. If Turkey receives S-400s, the F-35 transfers will be stopped and that would be a big loss,” Ian Lesser, executive director for Brussels bureau of the German Marshall Fund, told a panel hosted by the Foundation for Political, Economic and Social Research (SETA). Turkey's Permanent Representative to NATO Basat Ozturk said that Ankara has been contributing to all of NATO's missions, ranging from Afghanistan to Kosovo. Turkey is the second largest army in NATO and its contributions cannot be overlooked, Ozturk added. Turkey is preparing to receive the S-400 systems at the end of 2019, while being in a deal with the U.S. for procurement of the F-35 aircraft. However, the U.S. believes that S-400 will pose a threat to its F-35 fighter jets. The U.S. announced on April 1 that it has suspended "deliveries and activities" related to Turkey's procurement of the F-35 fifth-generation stealth fighter jet over Ankara's plans to buy Russia’s S-400. [AA, 28 May 2019]