Syria inadvertently shot down a Russian military plane after an Israeli attack on Syrian positions, killing 15 people on board, Moscow said.
Russian state media said Syrian anti-aircraft missiles shot the maritime patrol aircraft down amid an attack by Israeli jets in the Latakia region of north-west Syria.
Moscow blamed Israel for putting its aircraft in the line of fire and said it only had a minute's notice of the strike.
"As a result of the irresponsible actions of the Israeli military, 15 Russian servicemen were killed, which is absolutely not in keeping with the spirit of Russian-Israeli partnership," said Russian Maj. Gen. Igor Konashenkov, spokesperson for the Russian military, according to RIA-Novosti.
In a rare acknowledgment of its military activity in the region, Israel expressed "sorrow" for the loss of Russian life, but blamed the Syrian regime of Bashar al-Assad. The IDF said it had followed well-established protocols in communicating with Moscow, which are intended to prevent such incidents.
"Israel holds the Assad regime, whose military shot down the Russian plane, fully responsible for this incident," the IDF said in a statement, adding that Iran and Hezbollah were also accountable.
According to the statement, Syrian anti-aircraft batteries "fired indiscriminately and from what we understand did not bother to ensure no Russian planes were in the air."