President Vladimir Putin on Wednesday ordered state-of-the art air defense missile systems to be deployed at a Russian air base in Syria following the downing of one of its warplanes by Turkey, a move that raised the threat of a military confrontation between the NATO member and Moscow.

The S-400 missile systems will be sent to the Hemeimeem air base in Syria’s coastal province of Latakia, about 50 kilometers (30 miles) south of the border with Turkey. The systems have a range up to 400 kilometers (250 miles) and are capable of targeting Turkish jets with deadly precision. If Russia shot down a Turkish plane, Turkey could proclaim itself under attack and call for military assistance from its NATO allies.

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

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.

He said a warning from the Russian Foreign Ministry for Russians not to visit Turkey was needed “because we can’t exclude some other incidents following what happened yesterday and our citizens in Turkey could be in significant danger.”