President Vladimir Putin called Turkey's downing of a Russian fighter jet "a stab in the back" carried out by the accomplices of terrorists, saying the incident would have serious consequences for Moscow's relations with Ankara.
Speaking in the Russian Black Sea resort of Sochi before a meeting with Jordan's King Abdullah, Putin said the downed plane, which Turkey said it had repeatedly warned, had been attacked inside Syria when it was 1 kilometer from the Turkish border and had come down 4 kilometers inside Syria, according to Reuters.
The incident happened after it reportedly entered Turkish airspace increasing tensions between the two countries.
A Pentagon spokesman confirmed there was no U.S. involvement in Tuesday morning's Turkey-Russia jet incident.
Turkish President Recep Tayyip Erdoğan said the downing of the jet was fully in line with Turkey's rules of engagement, and that nobody should doubt his nation made all efforts to avoid incident along the border.
State-run Turkish news service Anadolu Agency said that the downed warplane was a Russian-made SU-24 and had been engaged by two Turkish F16 jets. The Turkish F16s warned the jet over the airspace violations before shooting it down, the military official told Reuters.
A U.S. military spokesperson confirmed later that Turkey had warned the Russian pilots repeatedly before it was shot down, and had received no response. U.S. defense officials also told NBC News that it wasn't clear that the plane was in Turkish airspace when it was shot down. The officials claimed that the incursion into Turkish airspace amounted to only a matter of seconds before it was shot down.
The Associated Press later cited U.S. and NATO officials as saying the jet had entered Turkish airspace before it was shot down.
Russia's defense ministry rejected Turkey's version of events, saying the downed fighter jet had not violated Turkish airspace. It said in a statement that the plane had been flying at an altitude of 6,000 meters and was "supposedly shot down from the ground." It emphasized that the plane was within Syrian airspace.
Kremlin spokesman Dmitry Peskov called the downing of the SU-24 a "very serious incident" but said it was too early to draw conclusions, Reuters reported.
Footage from Turkey's Anadolu Agency showed two pilots parachuting out of the jet before it crashed. A spokesman for the anti-Assad rebels in the area told NBC News that some of its fighters had opened fire on the pilots as they fell to the ground, killing one of them. The body was being held by the rebels, according the commander Jahid Ahmed, who added that he had no information on the second pilot.
Broadcast media has shown footage of Russian helicopters above the crash site. Later on Tuesday, Turkish officials said they believed that the Russian pilots were still alive and were working to secure their release.
Turkey is a member of the military alliance NATO which has said it is ready to defend Turkey if Russia violated its airspace, the BBC reported.
Turkish representatives briefed NATO ambassadors about the events surrounding the incident at 4.00 p.m. London time, Reuters reported. It is the first time a NATO member has downed a Russian or Soviet military aircraft since the 1950s, the news agency added.
NATO Secretary General Jens Stoltenberg said after the extraordinary meeting that the treaty organization stands in solidarity with Turkey in support of its territorial integrity. Stoltenberg said the information provided to NATO from several allied nations was all consistent with the Turkish account of events.
While calling for calm and "deescalation," Stoltenberg emphasized that the common enemy is the Islamic State, and admitted that most of Russia's attacks in Syria have been in areas where the extremist group is not operating.
The incident is set to increase tensions between Russia and Turkey who are both carrying out airstrikes in Syria as part of an alliance fighting the terrorist group that calls itself Islamic State.
Defense consultant Paul Beaver told CNBC that the downing of the jet was an incident that had been "waiting to happen."
"The Russians are very cavalier in the way they operate their aircraft," he told CNBC Tuesday. "Traditionally, they've always been less than scrupulous in terms of air traffic management. Given that, I feel that this incident was inevitable."
Beaver added that he had been informed by a source, who he declined to name, that the Russian jet was attacking an anti-Assad group that was backed by Turkey. CNBC was unable to reach the Russian Ministry of Defense for comment.
Both Russia and its ally, Syria's government, have carried out strikes in the area.
Footage from private broadcaster Haberturk TV showed a warplane going down in flames in a woodland area, a long plume of smoke trailing behind it. The plane went down in area known by Turks as "Turkmen Mountain" in northern Syria near the Turkish border, Haberturk said.
The next big issue is what the Russia's reaction could be to the shooting down of one of its aircraft. Beaver, who also advises the U.K. government on defense matters, said that NATO doesn't necessarily have a role to play unless Turkey asks it to.
"The Russian reaction will depend on what has happened to the air crew involved. If they're unharmed it should be fine. If they are harmed, then Russia's reaction will be hard and heavy."
Russia's state tourism agency Rostourism is recommending suspending sales of tour packages to Turkey following the incident, according to Reuters, and Sergei Lavrov, the Russian foreign minster, has canceled his trip to the country, according to the Interfax news agency.
— The Associated Press and Reuters contributed to this report.