Turkish fighter jets shot down a Russian warplane, with Ankara saying the aircraft had violated the country’s airspace, while Moscow said it had never strayed from Syrian territory and Russian President Vladimir Putin called the incident "a stab in the back."
One of the jet's two crew members was killed in the November 24 incident, which Putin called a crime, saying it would have "serious consequences" for relations between Russia and NATO-member Turkey. Russia is a major backer of Syrian President Bashar al-Assad’s government, and Turkey is one of its most vocal critics.
"We will never tolerate crimes like the one committed today," the Russian president said.
Another Russian serviceman on a helicopter search-and-rescue mission to find the downed pilots was also killed, military officials said.
With Russian, U.S., NATO, Syrian and other nations’ aircraft flying combat sorties over Syria, experts had long warned of the possibility of an aerial confrontation. The shoot-down was likely to worsen relations between Moscow and the Western alliance, already tense over Russian actions in Ukraine.
The clash was the first in decades between NATO forces and those of Russia or the Soviet Union, and comes amid an increasing number of near-miss incidents involving NATO and Russian aircraft around the world. One of the most recent exchanges of hostile fire was the 1970 downing of a U.S. spy plane, hit by a Soviet missile after it allegedly violated the airspace of what is now Armenia.
WATCH: Putin Calls Downing Of Jet 'Stab In The Back'
Despite angry rhetoric from Putin and other Russian officials, it was unclear how aggressively Moscow was prepared to respond to the November 24 downing.
The Russian Defense Ministry said the guided-missile cruiser Moskva, which carries the sophisticated S-300 antiaircraft missile system, would be moved closer to the Syrian coast, and “all potentially dangerous targets will be destroyed.”
Military-to-military contacts with Ankara will also be suspended, Russian officials said, and Turkey's military attache in Moscow was summoned for an official protest.
The Su-24M was shot down with an air-to-air missile fired by a Turkish F-16, according to Russian, U.S., and Turkish officials.
"A Russian Su-24 plane was downed under the rules of engagement because it violated Turkish airspace despite warnings," the Turkish Presidency said. U.S. and Turkish military officials said two Turkish F-16s warned the jet 10 times.
Russian, Turkish, and Western military officials sharply disagreed, however, whether the Russian jet had in fact violated Turkish airspace. The Russian Defense Ministry maintained that "the plane was over Syrian territory throughout the flight" and said it crashed four kilometers from the Turkish border.
WATCH: Video Purports To Show Dead Russian Pilot
A Pentagon spokesman, Colonel Steve Warren, said there were two Su-24s that were confronted by the Turkish jets and one was hit. He said the incident occurred "at the border," but couldn't confirm the Russian jets had actually violated Turkish airspace.
Warren also confirmed that Turkish pilots issued 10 warnings to the Russian jets, but the Russian pilots did not respond.
Speaking at a meeting with Jordan's King Abdullah II in the Black Sea city of Sochi, Putin denounced the jet's downing.
"Today's loss is...a stab in the back that has been inflicted on us by accomplices of terrorism," he said.
"In any case, our pilots and our aircraft did not threaten the Turkish Republic in any way. This is obvious. They were conducting an operation in the battle against ISIS," Putin said, referring to Islamic State militants that Russia says are the main target of its weeks-long bombing campaign in Syria.
The Su-24's two crew members ejected and parachuted from the plane after it was hit, and one was killed by small-arms fire from the ground, said Lieutenant General Sergei Rudskoi, a spokesman for the Russian General Staff.
One video circulated on social media by a Syrian rebel group appeared to show a Russian pilot immobile and badly wounded on the ground, and an official from the group told Reuters he was dead. Another video that was played repeatedly on Russian television showed armed gunmen firing at a descending parachute that was claimed to be one of the Su-24 pilots.
The fate of the second Russian was unclear. Turkish media reported that one of the pilots had been captured by rebels fighting forces loyal to Assad.
WATCH: Turkoman Commander Claims His Men Killed Russian Pilots
In Brussels, ambassadors from NATO's 28 member states held an extraordinary meeting at Turkey's request.
After the meeting, NATO's civilian chief, Jens Stoltenberg, told reporters the alliance's conclusions about the location of the Russian jets were "consistent with the information we have been provided with from Turkey."
"As we have repeatedly made clear, we stand in solidarity with Turkey and support the territorial integrity of our NATO ally, Turkey," he said.
At a White House news conference with visiting French President Francois Hollande, U.S. President Barack Obama said Turkey had a right to defend its territory and its airspace, but he urged both Ankara and Moscow to prevent further escalation.
He also again criticized the Russian campaign in Syria, which U.S. and European officials have said has overwhelmingly targeted moderate Syrian rebels, rather than extremist groups.
"I do think that this points to an ongoing problem with the Russian operations, in the sense that they are operating very close to the Turkish border, and they are going after moderate opposition that are supported by not only Turkey but by a wide range of countries," Obama said.
"If Russia is directing its energies toward Daesh and ISIL, some of those conflicts or potentials for mistakes or escalation are less likely to occur," he said, using other acronyms for Islamic State.
Later in the day, the White House said Obama and his Turkish counterpart, President Recep Tayyip Erdogan, spoke by telephone and "agreed on the importance of deescalating the situation and pursuing arrangements to ensure that such incidents do not happen again."
Both the White House and Erdogan's office said that Obama expressed U.S. and NATO support for Turkey's right to defend its sovereignty.
Turkish reports said plane was downed over the border area between Turkey's southern Hatay Province, in an area populated by the Turkic-speaking Turkmen minority. The British-based Syrian Observatory for Human Rights said the jet crashed in the Turkomen Mountains region in the coastal province of Latakia.
The Turkomen Mountains region has been targeted by a Syrian government offensive over the past days, aided by Russian air strikes. Russian and Syrian jets have been conducting a heavy bombing campaign against targets in northern Syria.
In a related incident on November 24, a Russian Mi-8 helicopter searching for the downed pilots came under fire and made an emergency landing in Latakia Province, Rudskoi said, and a Russian Marine was killed, though it was unclear exactly how.
A Syrian rebel group claimed to have shot down the helicopter. A video circulating on social media showed a rebel fighter firing at an U.S.-made TOW antitank missile at a helicopter on the ground.
Russia has provided Assad's government with military and diplomatic support throughout the war, which began as public protests in 2011 and morphed into an all-out civil war. Moscow substantially stepped up its involvement on September 30, launching a campaign of air strikes targeting Assad's opponents.
Turkey, like Western and Gulf Arab states, wants Assad out of power and has denounced the bombing campaign as a move to prop up the Syrian president. Turkish officials say the offensive has also displaced thousands of ethnic Turkomen Syrians.
Russia insists that its campaign is largely aimed against Islamic State militants, who are also the target of air strikes conducted by a U.S.-led coalition. Islamic State claimed responsibility for the downing of a Russian passenger jet in Egypt on October 31, killing all 244 people on board.
Putin has accused the United States and its allies of having double standards about terrorism, and has called on Washington and the West to accept Russia as an ally in the fight against Islamic State. He repeated those calls after the terrorist attacks that killed 130 people in Paris on November 13.
The November 24 incident was at least the third time that Russian jets have reportedly entered Turkish airspace. The previous incidents both sparked angry protests from Turkish authorities.
The Turkish military last month also shot down a drone that had entered its airspace. Moscow denied the drone belonged to its forces.
Russian Foreign Minister Sergei Lavrov, meanwhile, canceled a visit to Turkey scheduled for November 25. The effort was intended to mend ties between Moscow and Ankara and narrow the countries' differences on the Syrian conflict.
With reporting by RFE/RL’s Rikard Jozwiak and from Reuters, AP, AFP, dpa, Interfax, and TASS