The delivery of a second batch of Russian S-400 missile defense systems to Turkey may be delayed beyond a planned 2020 timeline, a senior Turkish official says.

Russia has taken a battalion of S-400 missile system to Serbia for joint military exercise, the interceptors’ first ever drill abroad.

A senior Russian military figure says Moscow and Ankara are in talks over a new deal for advanced Russian-made S-400 missile defense systems.

The likelihood of a new contract for the delivery of Russian air defense missile systems is high, Moscow says.

A senior Russian official says Moscow and Ankara are having “progressive interaction” about the possible sale of the Russian-made Sukhoi Su-35 fighter jets to Turkey.

The second part of the shipments began on August 27.

Turkish President Recep Tayyip Erdogan says he will discuss with his American counterpart, Donald Trump, a possible purchase of US-made Patriot surface-to-air missile systems in an upcoming meeting.

The Turkish president says his country is looking for alternatives to the US F-35 fighter jets.

The US House Foreign Affairs Committee says President Donald Trump must impose sanctions on Turkey over its purchase of Russian S-400 missile defense systems.

Deliveries of the advanced system are set to continue until April 2020.