By Dominic Evans and Khaled Yacoub Oweis
BEIRUT (Reuters) -- Syria warned on Thursday of a possible "surprise" response to Israel's attack on its territory and Russia condemned the airstrike as an unprovoked violation of international law.
Damascus could take "a surprise decision to respond to the aggression of the Israeli warplanes", Syrian ambassador to Lebanon Ali Abdul-Karim Ali said a day after Israel struck against Syria.
"Syria is engaged in defending its sovereignty and its land," Ali told a website of the Lebanese group Hezbollah. Syria and Israel have fought several wars and in 2007 Israeli jets bombed a suspected Syrian nuclear site, without a military response from Damascus.
Diplomats, Syrian rebels and regional security sources said on Wednesday that Israeli jets had bombed a convoy near the Lebanese border, apparently hitting weapons destined for Hezbollah. Syria denied the reports, saying the target had been a military research center northwest of Damascus.
Hezbollah, which has supported Syrian President Bashar Assad as he battles an armed uprising in which 60,000 people have been killed, said Israel was trying to thwart Arab military power and vowed to stand by its ally.
"Hezbollah expresses its full solidarity with Syria's leadership, army and people," said the group which fought an inconclusive 34-day war with Israel in 2006.
Israel has remained silent on the attack and there has been little reaction from its Western backers, but Syria's allies in Moscow and Tehran were quick to denounce the strike.
Russia, which has blocked Western efforts to put pressure on Syria at the United Nations, said that any Israeli airstrike would amount to unacceptable military interference.
"If this information is confirmed, then we are dealing with unprovoked attacks on targets on the territory of a sovereign country, which blatantly violates the UN Charter and is unacceptable, no matter the motives to justify it," the Foreign Ministry said in a statement.
Iranian deputy foreign minister Hossein Amir Abdullahian said the attack "demonstrates the shared goals of terrorists and the Zionist regime", Fars news agency reported. Assad portrays the rebels fighting him as foreign-backed, Islamist terrorists, with the same agenda as Israel.
"It is necessary for the sides which take tough stances on Syria to now take serious steps and decisive stances against this aggression by Tel Aviv and uphold criteria for security in the region," Abdullahian said.
An aide to Supreme Leader Ayatollah Ali Khamenei said on Saturday that Iran would consider any attack on Syria as an attack on itself, but Abdullahian made no mention of retaliation.
Hezbollah said the attack showed that the conflict in Syria was part of a scheme "to destroy Syria and its army and foil its pivotal role in the resistance front (against Israel)".Blasts shook district
Details of Wednesday's strike remain sketchy and, in parts, contradictory. Syria said Israeli warplanes, flying low to avoid detection by radar, crossed into its airspace from Lebanon and struck the Jamraya military research center.
But the diplomats and rebels said the jets hit a weapons convoy heading from Syria to Lebanon, apparently destined for Assad's ally Hezbollah, and the rebels said they -- not Israel -- hit Jamraya with mortars.
The force of the dawn attack shook the ground, waking nearby residents from their slumber with up to a dozen blasts, two sources in the area said.
"We were sleeping. Then we started hearing rockets hitting the complex and the ground started shaking and we ran into the basement," said a woman who lives adjacent to the Jamraya site.
The resident, who declined to be named because of the sensitivity over Israel's reported strike on Wednesday morning, said she could not tell whether the explosions which woke her were the result of an aerial strike.
Another source who has a relative working inside Jamraya reported that a building inside the complex had been cordoned off after the attack and that flames were seen rising from the area after the attack.
"It appears that there were about a dozen rockets that appeared to hit one building in the complex," the source, who also asked not to be identified, told Reuters. "The facility is closed today."
Israeli newspapers quoted foreign media on Thursday for reports on the attack. Journalists in Israel are required to submit articles on security and military issues to the censor, which has the power to block any publication of material it deems could compromise state security.
Syrian state television said two people were killed in the raid on Jamraya, which lies in the 25-km strip between Damascus and the Lebanese border. It described it as a scientific research center "aimed at raising the level of resistance and self-defense".
Diplomatic sources from three countries told Reuters that chemical weapons were believed to be stored at Jamraya, and that it was possible that the convoy was near the large site when it came under attack. However, there was no suggestion that the vehicles themselves had been carrying chemical weapons.
"The target was a truck loaded with weapons, heading from Syria to Lebanon," said one Western diplomat, echoing others who said the convoy's load may have included anti-aircraft missiles or long-range rockets.
The raid followed warnings from Israel that it was ready to act to prevent the revolt against Assad leading to Syria's chemical weapons and modern rockets reaching either his Hezbollah allies or his Islamist enemies.
A regional security source said Israel's target was weaponry given by Assad's military to fellow Iranian ally Hezbollah.
"This episode boils down to a warning by Israel to Syria and Hezbollah not to engage in the transfer of sensitive weapons," the source said. "Assad knows his survival depends on his military capabilities and he would not want those capabilities neutralized by Israel -- so the message is this kind of transfer is simply not worth it, neither for him nor Hezbollah."
Such a strike or strikes would fit Israel's policy of pre-emptive covert and overt action to curb Hezbollah and does not necessarily indicate a major escalation of the war in Syria. It does, however, indicate how the erosion of the Assad family's rule after 42 years is seen by Israel as posing a threat.
Israel this week echoed concerns in the United States about Syrian chemical weapons, but its officials say a more immediate worry is that the civil war could see weapons that are capable of denting its massive superiority in airpower and tanks reaching Hezbollah; the group fought Israel in 2006 and remains a more pressing threat than its Syrian and Iranian sponsors.