Russia has blamed Israel for the shutting down of one of its military planes and the deaths of the 15 personnel on board.
The Russian defence ministry said Israeli jets put the Il-20 plane into the path of Syrian air defence systems on Monday after failing to give Moscow enough warning of a strike on Syrian targets.
The Il-20 disappeared off the radar at about 23:00 local time (20:00 GMT).
Israel is yet to comment on the allegations.
According to reports, Monday’s incident occurred about 35km (22 miles) from the Syrian coast as the Ilyushin Il-20 aircraft was returning to Russia’s Hmeimim airbase near the north-western city of Latakia.
Russia’s Tass news agency says the Il-20 plane “disappeared during an attack by four Israeli F-16 jets on Syrian facilities in Latakia province”.