ISTANBUL: Ankara’s purchase of Russia’s S-400 missile defense system is a done deal, Turkish Foreign Minister Mevlut Cavusoglu said Tuesday, despite Washington’s efforts to persuade Turkey to buy the U.S. Patriot system instead.U.S. and NATO officials have warned Ankara that the Russian system cannot be integrated into the NATO air and missile defense system and that purchasing the S-400 system would jeopardize Turkey’s purchase of Lockheed Martin Corp F-35 fighter jets and possibly result in U.S. sanctions.