MOSCOW (AP) -- 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, just 50 kilometers (30 miles) away from the border with Turkey, are capable of striking targets within a 400-kilometer (250-mile) range with deadly precision. The military also moved the navy missile cruiser Moskva closer to the shore to help protect Russian warplanes with its long-range Fort air defense system.

"It will be ready to destroy any aerial target posing a potential danger to our aircraft," Russian Defense Minister Sergei Shoigu said at a meeting with military officials. He also announced the severance of all military ties with Turkey and said that from now on, Russian bombers will always be escorted by fighters on combat missions over Syria.

Ozgur Unluhisarcikli, director of the German Marshall Fund in Ankara, said it is possible Russia could down a Turkish plane.

"Turkish planes violate the Syrian border daily, either for reconnaissance flights or for anti-IS operations," he said. "In the same way that Turkey argues it has rules of engagement, Russia could also declare its own rules of engagement, saying it has the right to protect the skies of its ally."

The Russian plane's downing marked a dramatic turnaround in relations between Russia and Turkey, who have proclaimed themselves to be "strategic partners" in the past and developed booming economic ties despite differences over Syria.

Putin described the Turkish action as a "crime" and a "stab in the back," and called Turkey an "accomplice of terrorists." In a sign of the escalating tensions, protesters in Moscow hurled eggs and stones at the Turkish Embassy, breaking windows in the compound. Police cleared the area and made some arrests shortly after the protest began.

Turkish President Recep Tayyip Erdogan, who has often been compared to Putin for his authoritarian ways, said Wednesday that his country doesn't wish to escalate tensions with Russia.