President Vladimir Putin said on Tuesday that the shooting down of a Russian military plane near Syria's seacoast was the result of a chain of tragic and chance circumstances.
Russia's Defence Ministry said earlier that the aircraft was shot down by Syrian anti-aircraft systems, but accused Israel of indirectly causing the incident, saying Israeli jets nearby had put the Russian plane in the path of danger.
The ministry threatened to retaliate over what it called a hostile act. Putin's comments, made after talks with Hungary's prime minister in Moscow, appeared to somewhat defuse the situation though he said Russia needed to look further into what happened.
"I 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," Putin told reporters.
Putin said Moscow's response would aim at securing the safety of Russian military personnel in Syria's complex civil war in which various outside powers have backed opposing sides.
"As for retaliatory measures, they will be aimed first and foremost at further ensuring the safety of our military personnel and facilities in Syria. And these will be steps that everyone will notice," he said.
Russia's Defence Ministry said the Il-20 reconnaissance aircraft, with 15 Russians on board, was downed by anti-aircraft guns of Moscow's ally, Syria, in a "friendly fire" incident.
But the ministry said it held Israel responsible because, at the time of the incident, Israeli jets were attacking Syrian targets and had only given Moscow one minute's warning, putting the Russian aircraft in danger of being caught in cross-fire.
"We view the actions of the Israeli military as hostile," Russian Defence Ministry spokesman Igor Konashenkov told Russian state television.
"As a result of the irresponsible actions of the Israeli military, 15 Russian service personnel perished."
At a monthly UN Security Council meeting on Syria, US adviser on Syria, James Jeffrey, expressed "sorrow to our council partners Russia for the tragic loss of life ..."
"The unfortunate incident reminds us of the need to find a permanent, peaceful, and political resolution to the conflict."
Israel blames 'inaccurate' Syrian fire
In a statement, the Israel Defense Forces (IDF) expressed sorrow at the deaths but blamed the Syrian government and its allies Iran and Hezbollah.
The IDF said the initial Israeli inquiry into the incident found "extensive and inaccurate" Syrian surface-to-air 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.
An Israeli diplomatic source said Prime Minister Benjamin Netanyahu was expected to speak shortly with Putin.
After the incident, Russian Defence Minister Sergei Shoigu told his Israeli counterpart, Avigdor Lieberman, that Moscow held Israel wholly responsible, Russian news agencies reported.
Israel's Foreign Ministry said its deputy ambassador in Moscow had been summoned to the Russian Foreign Ministry but gave no details of what was discussed.
The Russian Ministry said the meeting was to do with the loss of the Russian plane.
Russian blind eye
Any row between Israel and Russia could curb Israel's ability to carry out air strikes inside Syria on what it sees as the greatest threat to its security from Syria's war - build-ups of Iranian forces or groupings of the Iranian-backed Hezbollah.
Since intervening in Syria in 2015, Russia has usually turned a blind eye to these attacks. Israel has launched about 200 such raids in the last two years, Israeli officials say.
Amos Yadlin, director of Tel Aviv University's Institute for National Security Studies, said on Twitter the downing of the Russian plane could "limit the bid to stop Iran’s entrenchment in Syria and the transfers of advanced weapons to Hezbollah."
Moscow said its plane disappeared from radar as it came into land at the Hmeymim air base in western Syria late on Monday. According to the Russian Defence Ministry, the Israeli F-16 jets carrying out the air strikes used the Russian plane as cover to allow them to approach their targets on the ground without being hit by Syrian fire.
"Hiding behind the Russian aircraft, the Israeli pilots put it in the line of fire of Syrian anti-aircraft systems. As a result, the Il-20... was shot down by the (Syrian) S-200 missile system," the ministry's Konashenkov said.
He said the Israeli pilots "could not have failed to see the Russian aircraft, as it was coming in to land from a height of 5km (three miles). Nevertheless, they deliberately carried out this provocation," Konashenkov said. "This absolutely does not correspond to the spirit of Russian-Israeli partnership."
The Israel military said that overnight its fighter jets had "targeted a facility of the Syrian Armed Forces from which systems to manufacture accurate and lethal weapons were about to be transferred on behalf of Iran to Hezbollah in Lebanon".
It said the weapons targeted in the Mediterranean coastal city of Latakia "were meant to attack Israel and posed an intolerable threat against it".
The IDF said the "deconfliction" system used by Israel and Russia "was in use tonight", adding: "Israel will share all the relevant information with the Russian government to review the incident and to confirm the facts in this inquiry."
Several countries have military operations underway around Syria, with forces on the ground or launching strikes from the air or from ships in the Mediterranean. In some cases, those countries are backing opposing sides in the Syrian war.
Foreign powers involved in the conflict - including Israel and Russia - operate hotlines to exchange operational details to avoid one side accidentally attacking the other's forces.
However, diplomats and military experts have warned that the risk of inadvertent strikes is high.
Turkey said on Tuesday it would send more troops into Syria's Idlib province after striking a deal with Russia that has averted a government offensive there.