Israel believes Hezbollah has restocked its arsenal with tens of thousands of rockets and missiles since a 2006 war between the two ended in a stalemate.
Israel is concerned that Hezbollah will take advantage of the chaos in Syria to smuggle advanced weapons into Lebanon.
These include anti-aircraft missiles, which could hamper Israel's ability to operate in Lebanese skies, and advanced Yakhont missiles that are used to attack naval ships from the coast.
In recent days, there were signs of mounting tensions between Israel and Hezbollah.
In a warning to Israel earlier this week, Hezbollah chief Hassan Nasrallah said his militia "is ready and has its hand on the trigger" in the event of an Israeli attack on any targets in Lebanon.
The Israeli military, meanwhile, called up several thousand reservists earlier this week for what it called a "surprise" military exercise on its border with Lebanon.
Details about Friday's strike remained sketchy.
The U.S. officials said the airstrike apparently hit a warehouse, but gave no other details.
Israeli officials did not say where in Syria the Israeli aircraft struck or whether they fired from Lebanese, Syrian or Israeli airspace.
Israel possesses bombs that can travel a long distance before striking their target. The use of such weapons could allow Israel to carry out the attack without entering Syrian skies, which would risk coming under fire from the regime's advanced, Russian-made anti-aircraft defenses.
The Syrian government said it had no information on an Israeli attack, while Hezbollah and the Israeli military spokesman's office declined comment.
Amos Gilad, an Israeli defense official, would not confirm or deny the airstrike, but played down cross-border tensions.
Hezbollah has not obtained any of Syria's large chemical weapons arsenal and is not interested in such weapons, Gilad said. Instead, the militia is "enthusiastic about other weapons systems and rockets that reach here (Israel)," he said Saturday in a speech in southern Israel.