Russian President Vladimir Putin, reacting to the shooting down of a Russian warplane by a Turkish interceptor, has warned of "serious consequences" for what he termed "a stab in the back".

He said the plane had been attacked when it was 1 km (0.62 mile) inside Syria.

"We will never tolerate such crimes like the one committed today," Putin said, as Russian and Turkish shares fell on fears of an escalation between the former Cold War enemies.

Each country summoned a diplomatic representative of the other and NATO called a meeting of its ambassadors for Tuesday afternoon. Russian Foreign Minister Sergei Lavrov canceled a visit to Turkey that had been due on Wednesday.

Footage from private Turkish broadcaster Haberturk TV showed the 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", it said.

Separate footage from Turkey's Anadolu Agency showed two pilots parachuting out of the jet before it crashed. A deputy commander of rebel Turkmen forces in Syria said his men shot both pilots dead as they came down.

A video sent to Reuters earlier appeared to show one of the pilots immobile and badly wounded on the ground and an official from the group said he was dead.

Russia's defense ministry said one of its Su-24 fighter jets had been downed in Syria and that, according to preliminary information, the pilots were able to eject.

"For the entire duration of the flight, the aircraft was exclusively over Syrian territory," it said.

The Turkish military said the aircraft had been warned 10 times in the space of five minutes about violating Turkish air space. Officials said a second plane had also approached the border and been warned.

"The data we have is very clear. There were two planes approaching our border, we warned them as they were getting too close," a senior Turkish official told Reuters.

"We warned them to avoid entering Turkish air space before they did, and we warned them many times. Our findings show clearly that Turkish air space was violated multiple times. And they violated it knowingly," the official said.

Turkey shot down a Russian warplane near the Syrian border on Tuesday, saying it had repeatedly violated its air space, one of the most serious publicly acknowledged clashes between a NATO member country and Russia for half a century.