Jim Heintz ?and Suzan Fraser

MOSCOW: Turkey shot down a Russian warplane on Tuesday that it said ignored repeated warnings and crossed into its airspace from Syria, killing at least one of the two pilots in a long-feared escalation in tensions between Russia and NATO. Russian President Vladimir Putin denounced what he called a “stab in the back” and warned of “significant consequences.”

The incident — the first time in half a century that a NATO member has downed a Russian plane — prompted an emergency meeting of the alliance. The incident highlighted the chaotic complexity of Syria’s civil war, where multiple groups with clashing alliances are fighting on the ground and the sky is crowded with aircraft bombing various targets.

“As we have repeatedly made clear we stand in solidarity with Turkey and support the territorial integrity of our NATO ally, Turkey,” NATO Secretary-General Jens Stoltenberg told a news conference after the meeting of the alliance’s decision-making North Atlantic Council, called at Turkey’s request.

The pilots of the downed Su-24 ejected, but one was killed by Syrian rebel fire from the ground as he parachuted to Earth, said the Russian general staff, insisting the Russian jet had been in Syrian airspace at the time. One of two helicopters sent to the crash site to search for survivors was also hit by rebel fire, killing one serviceman and forcing the chopper to make an emergency landing, the military said.

Stoltenberg urged “calm and de-escalation” and renewed contacts between Moscow and Ankara. Russia has long been at odds with NATO, which it accuses of encroaching on Russia’s borders, as well as with Turkey’s determination to oust Syrian President Bashar Assad, a longtime Moscow ally.

In Washington, President Barack Obama said Turkey “has a right to defend its territory and its airspace.”

Turkey said its fighter pilots acted after two Russian Su-24 bombers ignored numerous warnings that they were nearing and then entering Turkish airspace. In a letter to the U.N. Security Council and Secretary-General Ban Ki-moon, Turkey said the Russian warplanes violated its airspace “to a depth of 1.36 miles and 1.15 miles ... for 17 seconds” just after 9:24 a.m.

It said one of the planes then left Turkish airspace and the other one was fired at by Turkish F-16s “in accordance with the rules of engagement” and crashed on the Syrian side of the border.

Russia insisted the plane stayed over Syria, where it was supporting ground action by Syrian troops against rebels. Rebel forces fired at the two parachuting pilots as they descended, and one died, said Jahed Ahmad, a spokesman for the 10th Coast Division rebel group. The fate of the second pilot was not immediately known.