The Russian plane was used as cover by Israeli attackers and set up to be shot down in the counter-attack
Russia has told Israel it holds it responsible for the downing of its Il-20 maritime patrol aircraft by a Syrian missile. Russia told Israel that the latter knowingly used the larger Russian plane for cover and set it up to be shot down.
The Russians say Israel warned the attack was coming just one minute before it actually started, this left the Russian plane with no time to get out of the danger zone. Moreover, the Russian side (the Defense Minister) says it reserves the right to "respond":
“The blame for the downing of the Russian plane and the deaths of its crew members lies squarely on the Israeli side,” the Minister Shoigu said. “The actions of the Israeli military were not in keeping with the spirit of the Russian-Israeli partnership, so we reserve the right to respond.”
Spokesman Konashenkov reiterated the same point:
“We consider these provocative actions by Israel as hostile. Fifteen Russian military service members have died because of the irresponsible actions of the Israeli military. This is absolutely contrary to the spirit of the Russian-Israeli partnership,” the statement said. “We reserve the right for an adequate response.”
According to Russia the 4 attacking Israeli F-16s fired off their cruise missiles approaching from the same area the Il-20 was in but from attitude just above the sea so to Syrian radars the Russian plane would be the only one visible in the area where the missiles were coming from.
Israel has yet to publicly comment on the incident.