The Russian Defence Ministry says one of its jets has been shot down over Syria, and denies reports it violated Turkish air space.
Turkish officials said the downed plane was a Russian-made SU-24 which, after it entered Turkey's territory, was brought down by its F16s in line with its rules of engagement.
In a statement, the Turkish military said a foreign warplane was shot down after being warned 10 times in the space of five minutes.
An official told Reuters that two jets approached the border before one was shot down, and its data showed Turkish air space was repeatedly violated.
But quoted across various state-run media outlets, Russian defence officials said the plane was over Syria at the time - and that it appeared to have been shot down by artillery fire from the ground.
They said they could prove the plane was within Syrian territory "at all times".
"We are looking into the circumstances of the crash of the Russian jet," Russia's Defense Ministry said. "The Ministry of Defense would like to stress that the plane was over the Syrian territory throughout the flight."
Turkish media posted images and video showing the two pilots from the plane parachuting to the ground, while separate footage showed the jet itself crashing.
But the fate of the pilots remains unknown, and there were unconfirmed reports that they had been captured by either Turkmen or Nusra Front fighters.
Moscow said the pilots had parachuted away from the jet, but there had been no further contact with them since then.
The Syrian Observatory for Human Rights monitoring group said the warplane crashed in a mountainous area in the northern countryside of Latakia province.
President Tayyip Erdogan has been briefed by the head of the military and will talk to Prime Minister Ahmet Davutoglu, Turkish sources said.
