Damascus - Russia warned on Thursday that any Israeli air strike against Syria would be "unacceptable" after the Damascus regime said a military research centre had come under Israeli fighter jet attack.
Russia's foreign ministry said it was "deeply concerned" by the Syrian claims and that it was taking "urgent measures" to clarify the situation.
"If this information is confirmed, then we are dealing with unprovoked strikes against targets located on the territory of a sovereign state, which brazenly infringes on the UN Charter and is unacceptable, no matter the motive used for its justification," said a ministry statement.
The strident Russian statement came after the Syrian army accused Israel of launching a strike at dawn on Wednesday targeting its military research centre in Jamraya, near Damascus.
"Israeli fighter jets violated our airspace at dawn today and carried out a direct strike on a scientific research centre in charge of raising our level of resistance and self-defence," the general command said.
The warplanes entered Syria's airspace at low altitude and under the radar, the army said, adding that two site workers were killed.
"They... carried out an act of aggression, bombarding the site, causing large-scale material damage and destroying the building," state television quoted the military as saying.
Residents said six rockets hit the complex, leaving it partially destroyed, causing a fire and killing two people.
The army, meanwhile, denied reports that an Israeli air strike had targeted a weapons convoy from Syria near the border with Lebanon.
The attack came after Israel expressed concerns that Damascus's stockpile of chemical weapons could fall into the hands of Lebanon's Shi'ite Hezbollah group, an ally of Assad's regime, or other militant organisations.
Israel, whose officials have said such that a transfer would be a casus belli and likely spark an attack, has refused to comment on the attack.
The United States, which is currently hosting Israeli military intelligence chief Aviv Kochavi, also declined to comment.
Chemical weapons hit unlikely
As well as concerns about Syria's chemical weapons stockpile, Israel has accused Syria of supplying long-range Scud missiles to Hezbollah.
It has also warned about the dangers of other advanced weaponry falling into the Lebanese militia's hands, such as anti-aircraft systems and surface-to-surface missiles.
The attack took place just days after Israel moved two batteries of its vaunted Iron Dome missile defence system to the north and at a time of rising fears that the Syria conflict could see chemical weapons leaking into Lebanon.
A former intelligence chief with Israel's Mossad spy service said the Jewish state "should make any effort to prevent any weapons systems of that kind going out to terror organisations".
In comments before reports of the attack emerged, Amnon Sofrin said Israel was unlikely to hit chemical weapons stocks from the air because of the environmental risks.
"When you go and attack a... chemical weapons depot, you're going to do unwarranted damage because every part will leak out and can cause damage to many residents.
"But if you know of a convoy leading these kind of weapon systems from Syria to Lebanon, you can send a unit to the proper place and try to halt it" on the ground, he said.
Russia has outraged Western and Arab nations by refusing to join international calls for Syrian President Bashar Assad to step down and continues to supply its Soviet-era ally with weapons.
It has vetoed three Security Council resolutions sanctioning Assad for violence that the United Nations estimates has killed more than 60 000 people since it broke out in mid-March 2011.
A top Russian official on Thursday rejected the idea of the Security Council taking action because "the Council has already made a number of important decision" on Syria.
"I do not think that in current conditions, the UN Security Council will start work on a new resolution," Deputy Foreign Minister Gennady Gatilov told Russia's Interfax news agency.