Turkey received the first batch of Russia's S-400 missile  defense system on Friday, sparking NATO "concern" and risking deepening tensions with the US, which has repeatedly warned against the purchase. The delivery to an air base in the Turkish capital Ankara comes after Washington warned this week that there would be "real and negative" consequences if Turkey bought the defense system. 

NATO, which counts Turkey as one of its members, is "concerned about the potential ­consequences" of the purchase, an official told AFP. The alliance has repeatedly warned Turkey that the Russian system is incompatible with other NATO weapons systems, not least the F-35, a new generation multi-role stealth fighter jet.

The US fears that if Ankara integrates the S-400 into its defenses there is a risk that sensitive data about its F-35 could leak back to the Russians and it has threatened to expel Turkey from its fighter jet program.   

But Turkish President Recep Tayyip Erdogan has refused to back down and said he is confident Turkey will not face US sanctions.