Turkish warplanes have shot down a Russian military aircraft on the border with Syria.
Russian President Vladimir Putin said the Su-24 was hit by air-to-air missiles fired by Turkish F-16s while it was flying over Syrian territory.
But Turkish military officials said the plane was engaged after being warned that it was violating Turkish airspace.
Mr Putin described the incident as a “stab in the back” committed by “accomplices of terrorists”.
The crew ejected before the jet crashed in Latakia province, but Syrian rebels said at least one was dead.
It is the first time a Russian aircraft has crashed in Syria since Moscow launched air strikes against opponents of President Bashar al-Assad in late September.
The Nato military alliance, to which Turkey belongs, said it was following the situation “closely” and was in contact with the Turkish authorities. There will be an “informational meeting” of ambassadors in Brussels at 16:00 GMT.
‘Exclusively above Syria’
At a meeting with King Abdullah II of Jordan in Moscow, Russia’s president confirmed that the Su-24 had been shot down over Syrian territory, 1km (0.6 miles) from the Turkish border, by an air-to-air missile from a Turkish F-16 jet.
It crashed in Syrian territory 4km (2.5 miles) from the border, he added.
“Our pilots and our plane did not in any way threaten Turkey. It is quite clear,” Mr Putin stated.
“They were carrying out an operation against [Islamic State militants] in the mountains of northern Latakia, where militants who originate from Russian territory are concentrated. So they were carrying the key task of preventative attacks against those who could return to Russia at any time. ”