putin erdogan
The Russian president has met with his Turkish counterpart on the sidelines of the G20 to discuss bilateral relations and trade, including the purchase of S-400 missile defense systems, just ahead of Erdogan's meeting with Trump.

The delivery process of S-400 air defense systems is proceeding "without delays" and according to schedule, Erdogan confirmed, as he and Vladimir Putin touched upon Turkey's sovereign right to independently choose its defense suppliers, in defiance of massive pressure from Washington.

Erdogan stressed that Turkey values the deal because it comes with no strings attached and would potentially see joint production of anti-aircraft missiles, as well as technology transfer - something that the US has refused to provide.

Turkey and the US have been increasingly at odds over the conflict in Syria, and the S-400 deal, in particular. Ankara's defiance has already resulted in Washington suspending the delivery of F-35 fighter jets to Turkey, something Erdogan and Trump will likely discuss when they meet later on Saturday.