Russian President, Vladimir Putin, said a Russian warplane, 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.