Israel was tightlipped on Saturday following US media reports it had carried out an air strike on a Syrian weapons shipment headed for Shiite militant group and close Damascus ally Hezbollah in neighbouring Lebanon.
But officials reiterated that they were monitoring any possible transfer of game-changing arms to Lebanon.
CNN television said US and Western intelligence agencies were reviewing information suggesting Israel conducted the strike overnight on Thursday, as Israel was flying many warplanes over Lebanon and without entering Syrian airspace.
US officials told NBC News the air strikes most likely were targeting a shipment of weapons to Hezbollah, and a senior official told the network the warplanes were likely tied to delivery systems for chemical weapons.
The Israeli army would not comment, but a defence official stressed to AFP that "Israel 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 that Israel has conducted airstrikes on Syria this year.
Last month, Israeli Defence Minister Moshe Yaalon said Israel would not allow "sophisticated weapons" to fall into the hands of "Hezbollah or other rogue elements."
"When they crossed this red line, we acted," he said, in what was widely understood to refer to the air strike in January, which a US official told AFP had targeted surface-to-air missiles that Israel suspected were en route to Hezbollah.
The Shiite militant group has long been a close ally and client of the Syrian regime and also receives support from predominantly Shiite Iran.