Turkey-U.S. row over S-400 defense system escalates

The dispute over Turkey's purchase of the S-400 defense system has dragged on for two years. In 2017, Turkey and Russia signed a deal worth 2.5 billion U.S. dollars for the sale of the S-400 missile system. The U.S. strongly opposed the procurement by its NATO ally, saying the Russia-made system cannot be integrated into the NATO air defense system.