Israel was silent on Saturday on US media reports that it launched new air strikes on Syria targeting a weapons shipment to the Lebanese militant group Hezbollah.
The Israeli military and spokesmen for the defence ministry and prime minister's office declined to comment on the reports.
Israel and Hezbollah, a faithful ally of Syrian President Bashar al-Assad, fought a devastating war in the summer of 2006.
CNN television said US and Western intelligence agencies were reviewing information suggesting Israel conducted a strike overnight on Thursday.
A diplomatic source in Lebanon told AFP the operation destroyed surface-to-air missiles recently delivered by Russia that were being stored at Damascus airport.
Lebanon's army said pairs of Israeli airplanes entered Lebanese airspace three times overnight.
The first two entered over the southern city of Sidon at 7:10 PM (1610 GMT), followed three hours later by a second pair that entered over Jounieh north of Beirut, a statement said.
The last pair flew in over the capital, the statement said, adding that the warplanes stayed in Lebanese airspace for two to three hours at a time.
US media reported that Washington does not believe Israeli warplanes entered Syrian airspace to conduct the strikes.
A senior US official told NBC News that the air strikes were probably tied to delivery systems for chemical weapons.
But a senior Israeli defence official flatly rejected the notion that Hezbollah even wanted chemical weapons.
Amos Gilad said the militant Shiite group "is not eager to get its hands on those (chemical) arms. It is eager to take weapons systems like rockets."
"With chemical weapons it has problems," he said in remarks at a public event, relayed by Israeli media. "Chemical weapons can kill those who don't know how to use it too."
"I want to calm everyone here. Hezbollah doesn't have chemical weapons," he told the audience.
White House and Pentagon officials declined to comment on the air strike reports.
But Republican Senator Lindsey Graham of South Carolina, who serves on the Senate Armed Services Committee, was quoted as telling an audience that Israel had indeed bombed Syria.
"Israel bombed Syria tonight," Graham was cited by the Politico news website as saying in passing, without offering any further details.
The Israeli military on Saturday declined comment and a defence official said only that the Jewish state was monitoring any possible transfer of chemical weapons.
Israel is "following the situation in Syria and Lebanon, with an emphasis on transferring chemical weapons and special arms," the official told AFP.
If confirmed, this would be the second Israeli air strike on Syria this year.
Earlier this month, Israel implicitly admitted carrying out a January raid on a weapons convoy in Syria thought to be en route to Hezbollah.