The S-400 missile systems, which will be sent to the Hemeimeem air base in Syria's coastal province of Latakia, located just about 30 miles south of the border with Turkey, are capable of targeting Turkish jets with deadly precision. If Russia shot down a Turkish plane, NATO would officially be required to intervene on its behalf.

Turkey shot down a Russian Su-24 bomber Tuesday, saying it crossed into its airspace from Syria despite repeated warnings. One of its two pilots was killed by Syrian rebel fighters on the ground after bailing out, while his crewmate was rescued by Syrian army commandos and delivered in good condition to the Russian base.

Putin said the Russian plane remained in Syria's skies when it was shot down. He described Turkey's action as a "crime" and a "stab in the back," warning of serious consequences.