Russia has started delivering the second battery of its S-400 missile defense system to Turkey. The Turkish defense ministry said in a statement posted on Twitter that the shipment resumed Tuesday as Turkish media reported that a Russian cargo plane landed at an air base near Ankara. The delivery of the system has strained ties between Ankara and Washington. Turkey received the first battery of the Russian-made system last month, despite strong objections from its NATO ally, the United States. Washington says the Russian system is incompatible with NATO and poses a threat to the US-led F-35 fighter jet program. It suspended Turkeys participation in the F-35 program and has threatened sanctions against Ankara.