Russian President Vladimir Putin (REUTERS/Aleksey Druzhinin/RIA Novosti/Kremlin) Russian President Vladimir Putin (REUTERS/Aleksey Druzhinin/RIA Novosti/Kremlin)

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 shoot down — 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.”

At a news conference with French President Francois Hollande, he said the incident underscored the “ongoing problem” with Russia’s military operations in Syria, where the Russians have been targeting groups near the Turkish border. Calling Russia an “outlier” in the global fight against the Islamic State group, Obama said that if Moscow were to concentrate its airstrikes on IS targets, mistakes “would be less likely to occur.”

On Sept. 30, Russia began a campaign of massive airstrikes in Syria, which it says are aimed at destroying fighters of the Islamic State group but which Western critics contend are bolstering Assad’s forces.

Before Tuesday’s incident, Russia and the West appeared to be moving toward an understanding of their common strategic goal of eradicating IS, which gained momentum after the Nov. 13 attacks in Paris, as well as the Oct. 31 bombing of a Russian airliner over Egypt’s Sinai desert. The Islamic State group claimed responsibility for both attacks.

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.

A visibly angry Putin denounced what he called a “stab in the back by the terrorists’ accomplices” and warned of “significant consequences” for Russian-Turkish relations. Hours later Foreign Minister Sergey Lavrov cancelled a planned visit to Turkey on Wednesday.

Russia “will never tolerate such atrocities as happened today and we hope that the international community will find the strength to join forces and fight this evil,” Putin said.

Turkish Prime Minister Ahmet Davutoglu insisted his country had the right to take “all kinds of measures” against border violations, and called on the international community to work toward “extinguishing the fire that is burning in Syria.”

But despite the harsh words, some analysts believe that Russia and Turkey have reasons not to let the incident escalate, because of economic and energy ties and their common opposition to IS.

“Relations have been very strained between Russia and Turkey of late, so Moscow will be trying its utmost to contain the damage this might cause,” said Natasha Kuhrt, a lecturer in international peace and security at King’s College London.

A Turkish military statement said the Russian plane entered Turkish airspace over the town of Yayladagi, in Hatay province. Turkish officials released what they said was the radar image of the path the Russian plane took, showing it flying across a stretch of Turkish territory in the country’s southernmost tip.

Col. Steve Warren, spokesman for the U.S. military in Baghdad, said the U.S. heard communication between Turkish and Russian pilots and could confirm that Turkish pilots issued 10 verbal warnings before the plane was shot down.

A U.S. defense official in Washington said the Russian plane flew across a 2-mile section of Turkish airspace before it was shot down, meaning it was in Turkish skies for only a matter of seconds. The official, who was not authorized to discuss details of the incident, spoke on condition of anonymity.

Turkey has voiced concern over Russia’s bombing of ethnic Turkmen areas in Syria and complained that the Russian operations have complicated the possibility of creating a safe zone in northern Syria to protect civilians, as well as moderate rebels fighting Assad.

Syrian Turkmen are Syrian citizens of Turkish ethnicity who have lived in Syria since Ottoman times and have coexisted with Syrian Arabs for hundreds of years. They were among the first to take up arms against Syrian government forces, as Turkey lent its support to rebels seeking to topple Assad.

In late 2012, they united under the Syrian Turkmen Assembly, a coalition of Turkmen parties which represents Syrian Turkmens in the Western-backed Syrian National Coalition opposition group. The military wing of the assembly is called the Syrian Turkmen Brigades and aims to protect Turkmen areas from government forces and the Islamic State group.

Turkey has vowed to support the Syrian Turkmen and President Recep Tayyip Erdogan on Tuesday criticized Russian actions in the Turkmen regions, saying there were no Islamic State group fighters in the area.

Turkey has complained repeatedly that Russian planes supporting Assad are straying across the border. On Friday, Turkey summoned the Russian ambassador demanding that Russia stop operations in the Turkmen region.

Last month, Turkish jets shot down an unidentified drone that it said had violated Turkey’s airspace.

The country changed its rules of engagement a few years ago after Syria shot down a Turkish plane. According to the new rules, Turkey said it would consider all “elements” approaching from Syria an enemy threat and would act accordingly.

Following earlier accusations of Russian intrusion into Turkish airspace, the U.S. European Command on Nov. 6 deployed six U.S. Air Force F-15 fighters from their base in Britain to Incirlik Air Base in Turkey to help the NATO-member country secure its skies.

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