MOSCOW — In a move raising the potential threat of a Russia-NATO conflict, Russia said Wednesday it will deploy long-range air defense missiles to its base in Syria and destroy any target that may threaten its warplanes following the downing of a Russian military jet by Turkey.

The incident was the first time in half a century that a NATO member shot down a Russian plane. If Russia responds by downing a Turkish plane, NATO member Turkey could proclaim itself under attack and ask the alliance for military assistance.

Most observers believe that a direct military confrontation is unlikely, but that the shooting down of the plane will further fuel the Syrian conflict and complicate international peace efforts.

The situation is also alarming because the Russian and Turkish presidents both pose as strong leaders and would be reluctant to back down and seek a compromise.

The S-400 missiles, which Russian President Vladimir Putin ordered sent to the Hemeimeem air base in Syria’s coastal province of Latakia, 30 miles away from the border with Turkey, are capable of striking targets within a 250-mile range with deadly precision.