U.S. official: Israeli jets strike convoy in Syria

Syria, meanwhile, reported an Israeli strike targeting a research facility near the capital city of Damascus. State-run media said the attack killed two workers and injured five others.

"Israeli warplanes penetrated our airspace at dawn today and directly bombed one of the scientific research centers responsible for raising the level of resistance and self-defense in the area of Jimraya in the Damascus countryside," the military said in a statement aired on state-run TV Wednesday. "This comes after multiple failed attempts over months by terrorist groups to enter and seize the mentioned site."

It was not certain whether the U.S. and Syrian accounts of Israeli attack referred to the same or different incidents.

Israeli military and government officials declined to comment.

A former high-ranking Israeli Intelligence official told CNN that Hezbollah likely wants to take hold of all the weapons it can in the event that Syrian President Bashar al-Assad is forced to flee. Should al-Assad ultimately decide to leave, he may choose to further arm Hezbollah ahead of time so that militants could better attack Israel, the official said.

On Thursday, Hezbollah's TV station aired a statement condemning Israel's attack and calling it "barbaric."

"But, as usual, the international community has their tongue tied ... and will stay silenced without taking any further steps to condemn the attack or taking any serious position when Israel is the aggressor," the statement said.

In recent years, Syria transferred Scud missiles to Hezbollah that are capable of carrying chemical weapon warheads. But the senior U.S. official said American authorities do not believe the strike was linked to growing concerns about chemical weapons.

"We see no nexus," the official said Wednesday. The strike is thought to have hit a "target of opportunity," he said.

"Whether it was an attack against a supply convoy or a terrorist leader, it's not particularly surprising," senior Brookings fellow Michael O'Hanlon said. "At first glance, it likely won't be seen as a large escalation -- though there's still a possibility for retaliation."

The move came days after Russian Prime Minister Dmitry Medvedev said al-Assad's hold on power was "slipping away."

Russia, a power broker in the nearly 2-year-old conflict, has criticized Western powers, including the United States, that have recognized the opposition as Syria's rightful leadership.

There have been concerns about the security of Syria's chemical weapons arsenal, as well as the security of its larger conventional weapons.

Last month, NATO said Syria's government was "approaching collapse" and urged al-Assad to stop fighting and accommodate a political transfer of power.

The United States has provided more than $200 million in humanitarian aid and other funding to the Syrian opposition. On Tuesday, President Barack Obama approved another $155 million in aid.

The United States has pressed the Syrian opposition to establish a leadership structure amid a conflict that has claimed the lives of about 60,000 people, according to a United Nations estimate.

But Washington has been circumspect about its involvement in Syria. "We want to make sure that not only does it enhance U.S. security, but also that it is doing right by the people of Syria and neighbors like Israel that are going to be profoundly affected by it," Obama told CBS News' "60 Minutes."