Syrian regime defenses accidentally shot down on Monday a Russian military aircraft, in the deadliest known case of friendly fire between the two sides.
All 15 members of the jet were killed when regime defense swung into action against an Israeli missile strike, Russian and Israeli forces said Tuesday.
Russian President Vladimir Putin said it was the result of "tragic accidental circumstances".
His comments appeared to somewhat defuse a possible crisis involving outside powers that back opposing sides in Syria’s complex civil war, after Russia’s Defense Ministry accused Israel of indirectly causing the incident.
The ministry said that while Syrian anti-aircraft had mistakenly shot down the plane of a close ally, Israeli jets flying nearby had put the Russian jet in the path of danger, and it threatened to retaliate over what it called a hostile act.
Putin told reporters: “It looks most likely in this case that it was a chain of tragic chance events, because an Israeli aircraft did not shoot down our aircraft. But, without any doubt we need to seriously get to the bottom of what happened.
There was no immediate word from Damascus, but the deadly chain of events started when Israeli missiles struck the coastal region of Latakia on Monday.
Israel said it had targeted a Syrian regime facility where weapons manufacturing systems were "about to be transferred on behalf of Iran" to the Lebanese group “Hezbollah”.
Israel expressed "sorrow" for the Russian deaths, but insisted the Russian Ilyushin plane had been felled by "extensive and inaccurate Syrian anti-aircraft (surface-to-air missile) fire".
The Russian military accused Israeli pilots of using "the Russian plane as a cover, exposing it to fire from Syrian air defenses".
“We view the actions of the Israeli military as hostile,” Russian Defense Ministry spokesman Igor Konashenkov told Russian state television. “As a result of the irresponsible actions of the Israeli military, 15 Russian service personnel perished.”
Russia warned Israel of reprisals and summoned its envoy in Moscow.
Israel denied the accusations, saying its jets were already back in Israeli airspace when regime forces launched the missiles that hit the Russian plane.
In a statement the Israeli army voiced sorrow at the deaths but blamed the Syrian regime and its main regional allies Iran and “Hezbollah”.
It said the initial Israeli inquiry into the incident found “extensive and inaccurate” Syrian anti-aircraft fire “caused the Russian plane to be hit and downed”.
“The Syrian anti-air batteries fired indiscriminately and from what we understand, did not bother to ensure that no Russian planes were in the air,” the statement said.
It added that by the time the Russian plane was struck, the Israeli jets were already back in their own airspace. The Russian plane was “not within the area of the operation” carried out by the Israeli jets, it said.
After the incident, Russian Defense Minister Sergei Shoigu told his Israeli counterpart, Avigdor Lieberman, that Moscow held Israel wholly responsible, Russian news agencies reported.
The Syrian Observatory for Human Rights said some missiles, suspected to be Israeli, did get through the Syrian defenses and struck ammunition depots at the site of the technical industries institute.
Rami Abdel Rahman, the head of the Britain-based monitoring group, said at least two fighters were killed and 10 wounded in the strike.
Israel has conducted frequent raids in recent months against Syria's regime infrastructure, including against bases it believes host Iranian combatants.
Earlier in September, Israel admitted carrying out 200 strikes in Syria over the past 18 months.
