The leaders of Russia and Israel have sought to defuse tension after a Russian plane was shot down by Syrian forces amid an Israeli air raid.
In a call to Vladimir Putin, Israeli PM Benjamin Netanyahu expressed regret at the loss of 15 Russian personnel, but stressed again that Syria was to blame.
Mr Putin had earlier called the incident "a chain of tragic accidental circumstances".
The Il-20 plane was downed over the Mediterranean Sea on Monday evening.
Russia is supporting President Bashar al-Assad in Syria's civil war.
Mr Putin and Mr Netanyahu spoke by telephone, shortly after the Russian president had made his conciliatory statement in Moscow.
"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 the bottom of what happened," Mr Putin said at a media briefing.
Mr Netanyahu addressed that issue in the telephone call, offering to provide "all necessary information" in the investigation of the incident, as well as expressing regret over the fatalities.
In the call, Mr Putin urged Mr Netanyahu "not to let such a situation happen in the future" and told him Israeli air operations breached Syrian sovereignty, Russian media said.
Russia's Defence Minister Sergei Shoigu had earlier said Moscow "reserves the right to take further steps in response".
But Mr Putin said the "retaliatory measures" would be "aimed first and foremost at further ensuring the safety of our military personnel".
Russia's Tass news agency said an Ilyushin Il-20 reconnaissance plane had "disappeared during an attack by four Israeli F-16 jets on Syrian facilities in Latakia province".
The downing was reported to have occurred about 35km from the Syrian coast as the Il-20 aircraft was returning to Russia's Hmeimim airbase near Latakia.
The Israel Defense Forces (IDF) said its aircraft were targeting Syrian military facilities "from which systems to manufacture accurate and lethal weapons were about to be transferred on behalf of Iran to Hezbollah in Lebanon".
The Lebanese Shia militant group and Iran are both allies of the Syrian government. Israel has reportedly hit more than 200 Iranian targets in Syria over the past 18 months.
The Syrian Observatory for Human Rights monitoring group said some Israeli missiles did find the target and two people were killed on the ground. However, it could not confirm their identity and Syria has made no official comment.
How did the plane get shot down?
Both the Russians and Israelis agree it was Syrian anti-aircraft fire, although Syria has not commented.
Russia said it was given less than a minute's warning by Israel ahead of the strikes, which was not enough time to get the military surveillance plane out of the way.
It also said the Israeli planes had "used the Russian airplane as a cover", putting it "in the line of fire coming from Syrian air defence systems".
Israel disputes this. In a rare statement detailing its operations over Syria, the IDF said: "The Russian plane that was hit was not within the area of the operation... when the Syrian army launched the missiles that hit the Russian plane, (Israeli) jets were already within Israeli airspace."
The Russian defence ministry said body fragments, personal belongings and the plane's debris had been found by search ships in the Mediterranean on Tuesday.
The IDF said: "Israel holds the Assad regime, whose military shot down the Russian plane, fully responsible for this incident."
The statement also laid blame on Iran and Hezbollah.
In his phone call with Mr Putin, Mr Netanyahu insisted that Israel would continue to target Iran inside Syria.