The downing of a Russian fighter jet by Turkey raised the complex tensions around Syria’s multisided civil war to new heights Tuesday, putting more pressure on the Obama administration to take a more aggressive leadership role in the conflict to head off a further escalation between Moscow and Ankara.

An angry Russian President Vladimir Putin Tuesday afternoon called the shootdown “a stab in Russia’s back delivered by terrorist accomplices,” and asserted that “we will never tolerate such crimes like the one committed today.”

The Russian Defense Ministry denied that its aircraft had violated Turkish airspace and that Turkey refused to answer emergency communications trying to establish what had happened. The Foreign Ministry issued a statement urging Russians not to visit Turkey and canceled a planned meeting Wednesday between the Russian and Turkish foreign ministers.

SEE ALSO: Obama pokes Putin, says jet shoot-down part of ‘ongoing problem’ with Russians

“As [Mr. Putin] has said bluntly, this cannot but affect Russian-Turkish relations,” Russian Foreign Minister Sergey Lavrov said.

Turkey defended its action, saying in a letter to the U.N. Security Council that it fired only after two Russian Su-24 “Fencer” multirole attack jets had flown into Turkish airspace along the border with Syria and ignored repeated warnings to change direction.

This frame grab from video by Haberturk TV shows a Russian warplane ... more >

Two pilots who ejected from one of the Su-24s that was hit by Turkish F-16 fire were subsequently shot at by ethnic Turkmen rebels — allies of the Ankara government — on the Syrian side of the border as the pilots parachuted to the ground. Video of one, who reportedly died, quickly circulated on social media.

SEE ALSO: Pentagon backs Turkey’s version of events, blames ‘incursion’ of Russian jet

The Russian general staff confirmed that one of its pilots was killed by Syrian rebel fire from the ground as he parachuted to the ground. On Wednesday, Russia confirmed that the second pilot was rescued by the Syrian military and is safe.

One of two Russian 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, according to The Associated Press.

The incident marked the first time since the 1950s that a NATO member-country has publicly acknowledged shooting down a Russia military aircraft — the last time being at the end of the Korean War — and it quickly sparked fears of a Cold War-style standoff.

NATO’s governing body convened an extraordinary meeting in Brussels on Tuesday afternoon at Turkey’s request. And in Washington, President Obama echoed NATO Secretary-General Jens Stoltenberg in calling on Moscow and Ankara to communicate and “take measures to discourage any kind of escalation.”

Turkish President Tayyip Erdogan, whose country has enjoyed relatively cordial relations with Russia, told reporters in Ankara that “nobody should doubt that we made our best efforts to avoid this latest incident.”

Turkey’s military has been on edge for months over alleged Russian incursions into its airspace. Turkish jets shot down an unidentified surveillance drone on the Syrian border last month that was widely believed to have been operated by Moscow. And on Friday Ankara summoned the Russian ambassador apparently out of frustration over the airspace incursions.

The two powers have been on opposite sides of Syria’s war since it began in 2012, as Turkey supports opposition rebels fighting for the ouster of Syrian President Bashar Assad, while Moscow scrambles to defend its embattled ally in Damascus.

Tensions came to a boil in late-September, when Moscow opened a bombing campaign in Syria. While some Russian sorties have pounded territory held by the Islamic State — also known as ISIS and ISIL — in Syria a significant portion of the campaign has targeted the anti-Assad rebels backed not only by Turkey but also by Washington.

The Russian plane on Tuesday was supporting Syrian troops loyal to the Assad regime, which have been on the offensive in an area along the Turkish border controlled by several insurgent groups — including al Qaeda’s branch in Syria, the Nusra Front — as well as rebels with the U.S.- and Turkey-backed Free Syrian Army.

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