BEIRUT (AP) ― Israel launched a rare airstrike inside Syria, U.S. officials said Wednesday, targeting a convoy believed to contain anti-aircraft weapons bound for Hezbollah militants in Lebanon. The attack adds a potentially flammable new element to tensions already heightened by Syria’s civil war.

It was the latest salvo in Israel’s long-running effort to disrupt the Shiite militia’s quest to build an arsenal capable of defending against Israel’s air force and spreading destruction inside the Jewish state.

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.

U.S. officials said the target was a truck convoy that Israel believed was carrying sophisticated 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.

The officials spoke on condition of anonymity because they were not authorized to brief the media.

In a statement, the Syrian military denied the existence of any such shipment and said a scientific research facility outside Damascus was hit by the Israeli warplanes.

The Israeli military declined to comment. However, many in Israel worry that as Syrian President Bashar Assad loses power, he could strike back by transferring chemical or advanced weapons to Hezbollah, which is neighboring Lebanon’s most powerful military force and is committed to Israel’s destruction.

The airstrike 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 Assad regime and rebel brigades seeking his ouster.

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

A Syrian military statement read aloud on state TV Wednesday said low-flying Israeli jets crossed into Syria over the Israeli-occupied Golan Heights and bombed a military research center in the area of Jamraya, northwest of Damascus.

The strike destroyed the center and damaged a nearby building, killing two workers and wounding five others, the statement said.

The military denied the existence of any convoy bound for Lebanon, saying the center was responsible for “raising the level of resistance and self-defense” of Syria’s military.

“This proves that Israel is the instigator, beneficiary and sometimes executor of the terrorist acts targeting Syria and its people,” the statement said.

Israel and Hezbollah fought an inconclusive 34-day war in 2006 that left 1,200 Lebanese and 160 Israelis dead.

While the border has been largely quiet since, the struggle has taken other forms. Hezbollah has accused Israel of assassinating a top commander, and Israel blamed Hezbollah and Iran for a July 2012 attack on Israeli tourists in Bulgaria. In October, Hezbollah launched an Iranian-made reconnaissance drone over Israel, using the incident to brag about its expanding capabilities.

Israeli officials believe that Hezbollah’s arsenal has markedly improved since 2006, now boasting tens of thousands of rockets and missiles and the ability to strike almost anywhere inside Israel.

Israel suspects that Damascus obtained a battery of SA-17s from Russia after an alleged Israeli airstrike in 2007 that destroyed an unfinished Syrian nuclear reactor.

Earlier this week, Israeli Prime Minister Benjamin Netanyahu warned of the dangers of Syria’s “deadly weapons,” saying the country is “increasingly coming apart.”

The same day, Israel moved a battery of its new “Iron Dome” rocket defense system to the northern city of Haifa, which was battered by Hezbollah rocket fire in the 2006 war. The Israeli army called that move “routine.”

Syria, however, cast the airstrike in a different light, linked to the country’s civil war, which it blames on terrorists carrying out an international conspiracy.

Despite its icy relations with Assad, Israel has remained on the sidelines of efforts to topple him, while keeping up defenses against possible attacks.

Israeli defense officials have carefully monitored Syria’s chemical weapons, fearing Assad could deploy them or lose control of them to extremist fighters among the rebels.

President Barack Obama has called the use of chemical weapons a “red line” that if crossed could prompt direct U.S. intervention, though U.S. officials have said Syria’s stockpiles still appear to be under government control.

The strike was Israel’s first inside Syria since September 2007, when warplanes destroyed a site that the U.N. nuclear watchdog deemed likely to be a nuclear reactor. Syria denied the claim, saying the building was a non-nuclear military site.

Syria allowed international inspectors to visit the bombed site in 2008, but it has refused to allow nuclear inspectors new access. This has heightened suspicions that Syria has something to hide, along with its decision to level the destroyed structure and build on its site.

In 2006, Israeli warplanes flew over Assad’s palace in a show of force after Syrian-backed militants captured an Israeli soldier in the Gaza Strip.

And in 2003, Israeli warplanes attacked a suspected militant training camp just north of the Syrian capital, in response to an Islamic Jihad suicide bombing in the city of Haifa that killed 21 Israelis.

Syria vowed to retaliate for both attacks but never did.

In Lebanon, which borders both Israel and Syria, the military and the U.N. agency tasked with monitoring the border with Israel said Israeli warplanes have sharply increased their activity in the past week.

Israeli violations of Lebanese airspace are not uncommon, and it was unclear if the recent activity was related to the strike in Syria.

Syria’s primary conflict with Israel is over the Golan Heights, which Israeli occupied in the 1967 war. Syria demands the area back as part of any peace deal. Despite the hostility, Syria has kept the border quiet since the 1973 Mideast war and has never retaliated for Israeli attacks.

In May 2011, only two months after the uprising against Assad started, hundreds of Palestinians overran the tightly controlled Syria-Israeli frontier in a move widely thought to have been facilitated by the Assad regime to divert the world’s gaze from his growing troubles at home.