BEIRUT – Israel’s air force launched a rare airstrike on a military site inside Syria, the Syrian government and U.S. officials said Wednesday, adding a potentially flammable new element to regional tensions already heightened by Syria’s civil war.

The strike appeared to be the latest salvo in Israel’s long-running effort to disrupt the Lebanese militant group Hezbollah’s quest to build an arsenal capable of defending against Israel’s air force and spreading destruction inside the Jewish state.

U.S. officials said the target was a convoy of trucks that Israel believed contained anti-aircraft weapons bound for Hezbollah in Lebanon. They spoke on condition of anonymity because they were not authorized to speak about the operation.

Regional officials said the shipment included sophisticated Russian-made SA-17 anti-aircraft missiles, which if acquired by Hezbollah would be “game-changing,” enabling the militants to shoot down Israeli jets, helicopters and surveillance drones.

Regional security officials said the strike, which occurred overnight Tuesday, targeted a site near the Lebanese border, while a Syrian army statement said it destroyed a military research center northwest of the capital, Damascus. They appeared to be referring to the same incident.

The Israeli military and a Hezbollah spokesman both declined to comment, and Syria denied the existence of any such weapons shipment. All officials spoke on condition of anonymity because they were not authorized to brief the media.

The strike follows decades of enmity between Israel and allies Syria and Hezbollah, which consider the Jewish state their mortal enemy. The situation has been further complicated by the civil war raging in Syria between the forces of President Bashar Assad and rebel brigades seeking his ouster.

The war has sapped Assad’s power and threatens to deprive Hezbollah of a key supporter as well as its land corridor to Iran. The two countries provide Hezbollah with the bulk of its funding and arms.