Israeli warplanes have targeted a Syrian weapons shipment headed for Hezbollah in Lebanon, media quoted US officials as saying Saturday, as Sunnis were fleeing a city for fear of a massacre.
The news came as US President Barack Obama, under mounting criticism that he has allowed Bashar al-Assad's regime to cross his own declared "red line" on using chemical weapons, came close to ruling out deploying US troops to Syria.
CNN said US and Western intelligence agencies were reviewing information suggesting Israel had likely conducted a strike overnight on Thursday.
But the United States does not believe Israeli warplanes entered Syrian airspace to carry out the strikes, it added.
Lebanon's army said pairs of Israeli airplanes entered Lebanese airspace on three occasions on Thursday night and stayed for two to three hours at a time.
NBC cited US officials as saying it was believed the primary target was a weapons shipment headed for Hezbollah, the powerful Lebanese Shiite militant group closely allied to Assad's regime.
One said the raid was likely tied to delivery systems for chemical weapons, but CNN cited officials as saying there was no reason to believe Israel had struck chemical weapons storage facilities.
White House and Pentagon officials declined to comment and Israel was tightlipped on the reports.
An Israeli defence official stressed to AFP that the Jewish state "was following the situation in Syria and Lebanon, with an emphasis on transferring chemical weapons and special arms."
If confirmed, this would mark the second time Israel has hit Syria this year after it implicitly admitted carrying out a January strike on weapons thought to be en route to Hezbollah.
In Syria, hundreds of families were fleeing Sunni districts Banias city on Saturday, fearing new attacks after a "massacre" in a nearby Sunni village, a watchdog said.
"Hundreds of families are fleeing Sunni neighbourhoods in Banias in fear of a new massacre," said Rami Abdel Rahman of the Syrian Observatory for Human Rights.
The exodus comes after shelling on Sunni areas of the city on Friday, and reports of a "large-scale massacre" in a nearby Sunni village on Thursday.
Video from Ras al-Nabaa shot by activists and distributed by the Observatory showed a pile of bloodied bodies lying in a street, a least one of them that of a child.
The exodus follows reports of a "massacre" of at least 50 people in the Sunni village of Bayda, south of Banias.
The Observatory said the deaths were the result of summary executions and shelling.
The Banias region is a bastion of the Alawites, an offshoot of Shiite Islam and the sect to which Assad belongs, while the insurgents battling to topple his regime are mainly Sunni Muslims.
The opposition National Coalition denounced a "large-scale massacre" by regime forces on Thursday in Bayda, citing witness reports of civilians being stabbed to death.
State media said troops killed "terrorists" -- the regime term for insurgents -- in an operation targeting rebels.
Speaking in Costa Rica, Obama came close to ruling out deploying US troops to Syria, saying he did not foresee a scenario in which that would be beneficial to either country.
"As a general rule, I don't rule things out as commander-in-chief because circumstances change and you want to make sure that I always have the full power of the United States at our disposal to meet American national security interests," Obama said.
"Having said that, I do not foresee a scenario in which boots on the ground in Syria -- American boots on the ground in Syria-- would not only be good for America but also would be good for Syria."
Speculation has mounted the Obama administration could reverse its opposition to arming the rebels after the White House said last week Assad had likely used chemical weapons on his people.
In Latakia province, an Assad bastion, rebels from the Free Syrian Army are training for a prolonged guerrilla war against stubbornly resilient regime forces, who are better armed and have air superiority.
"We need anti-tank, anti-aircraft missiles, communication equipment, satellite technology to monitor the movement of regime fighters," said brigade commander Abu Basir.
"If we had these, the war would be over by now."
The US says the Syrian conflict, now in its third year, has killed more than 70,000 people.