Moscow was "deeply concerned" over reports of Israeli air strikes on Syrian territory and is seeking confirmation of what could be a serious violation of the UN charter, the Russian foreign ministry said Thursday.
Moscow said it is looking into reports that Israeli fighter jets carried out an air strike on a military research centre near Damascus Wednesday.
If the reports of "unprovoked strikes" hitting a sovereign country's territory are confirmed, this would constitute a violation of fundamental UN principles, the ministry said.
Such attacks are "unacceptable, no matter where their motivations lie".
Syrian state media, citing the army's general command, said the strikes killed at least two people.
Western media reports said Israeli jets bombed a convoy allegedly carrying weapons destined for Shia militant group Hezbollah, which has previously fired rockets into Israel from Lebanon.
In March 2012, Israel's Haaretz daily reported Syria had supplied Hezbollah with advanced Russian-made anti-aircraft missile systems and was training operators how to use them, in a move which could threaten Israeli air supremacy in the region.
In 2007, Israel carried out an air raid on Syria, hitting what it said was intended to be a nuclear reactor site.
It also destroyed an Iraqi nuclear reactor in a bombing raid in 1981.
Israel has not officially commented on the reported incident.
Earlier this week, Israeli officials voiced alarm over Syrian chemical or biological weapons possibly falling into the hands of Hezbollah or other militant groups which might use them against Israel.
The Russia foreign ministry also called for peaceful dialogue without foreign influence in Syria, where over 60,000 have died in almost two years of civil war.