Israel conducted a rare airstrike on a military target inside Syria near the border with Lebanon, foreign officials and Syrian state TV said Wednesday, amid fears President Bashar al-Assad's regime could provide powerful weapons to the Islamic militant group Hezbollah.

Regional security officials said Israel had been planning in the days leading up to the airstrike to hit a shipment of weapons bound for Hezbollah, Lebanon's most powerful military force and a sworn enemy of the Jewish state.

Among Israeli officials' chief fears is that Assad will pass chemical weapons or sophisticated anti-aircraft missiles to Hezbollah — something that could change the balance of power in the region and greatly hinder Israel's ability to conduct air sorties in Lebanon.

The regional officials said the shipment Israel was planning to strike included Russian-made SA-17 anti-aircraft missiles, which would be strategically "game-changing" in the hands of Hezbollah by enabling the group to carry out fiercer attacks on Israel and shoot down Israeli jets, helicopters and surveillance drones. A U.S. official said the strike hit a convoy of trucks but did not give an exact location.

The Syrian military confirmed the strike in a statement read aloud on state TV, but it said the jets bombed a military research centre in the area of Jamraya, northwest of the capital, Damascus, and about 15 kilometres from the border with Lebanon.

The statement said the centre was responsible for "raising the level of resistance and self-defence" of Syria's military. It said the strike destroyed the centre and a nearby building, killing two workers and wounding five others.

The Syrian army statement denied that the strike had targeted a convoy headed from Syria to Lebanon, instead portraying the strike as linked to the civil war pitting Assad's forces against rebels seeking to push him from power.

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

The Israeli military declined to comment, and the location could not be independently confirmed because of reporting restrictions in Syria.

Syria a longtime Hezbollah supporter

Hezbollah has committed to Israel's destruction and has gone to war against the Jewish state in the past. Syria has long been among the militant group's most significant backers and is suspected of supplying with funding and arms, as well as a land corridor to Iran.

This strike also comes as Syria is enmeshed in a civil war. The rebels have seized a large swath of territory in the country's north and established footholds in a number of Damascus suburbs, though Assad's forces still control the city and much of the rest of the country.

While Assad's fall does not appear imminent, analysts worry he could grow desperate as his power wanes and seek to cause trouble elsewhere in the region through proxy groups like Hezbollah.

Syria's government portrays the crisis, which started with political protest in 2011 and has since become a civil war, as a foreign-backed conspiracy meant to destroy the country.

Top Israeli officials have recently expressed worries that Assad's regime could pass chemical weapons to Hezbollah or other militant groups.

President Barack Obama has called Syria's use of chemical weapons a "red line" whose crossing could prompt a tougher U.S. response, but U.S. officials say they are tracking Syria's chemical weapons and that they still appear to be under regime control.

The strike, carried out either late Tuesday or early Wednesday, appears to be the latest move in a long running race by Hezbollah to increase its military power while Israel seeks to limit it.

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.

Iron Dome missile defence moved to northern Israel

Earlier this week, Israel moved a battery of its new "Iron Dome" rocket defence system to the northern city of Haifa, which was battered by Hezbollah rocket fire in the 2006 Israel-Hezbollah war. The Israeli army called that move "routine."

The airstrike was the first inside Syria in more than five years. In September 2007, Israeli warplanes destroyed a site in Syria that the U.N. nuclear watchdog deemed likely to be a secretly built nuclear reactor. Syria has 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 later build over it.

Israeli warplanes flew over Assad's palace in 2006 after Syrian-backed militants in Gaza captured an Israeli soldier.

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.

The military in Lebanon, which also shares a border with Israel, said Wednesday that Israeli warplanes have sharply increased their activity over Lebanon in the past week, including at least 12 sorties in less than 24 hours in the country's south.

A senior Lebanese security official said no Israeli airstrikes occurred inside Lebanese territory. Asked whether it could have been along the border on the Syrian side, he said that that could not be confirmed as it was out of his area of operations.

A Lebanese army statement said the last of the sorties took place at 2 a.m. local time Wednesday. It said four warplanes which flew in over the southernmost coastal town of Naqoura and hovered for several hours over villages in southern Lebanon before leaving Lebanese airspace.

It said eight other warplanes conducted similar flights on Tuesday.

Another Lebanese security official said the flights were part of "increased activity" in the past week but did not elaborate. He spoke on condition of anonymity because he was not authorized to brief the media.

All officials spoke on condition of anonymity because they were not authorized to discuss the strike.

The UN agency tasked with monitoring the Lebanon-Israeli border said in a statement Wednesday it had no information on any strikes near the Syria-Lebanon border. It did note, however, a "high number of Israeli overflights" on Tuesday.

"These air violations have continued on an almost daily basis," it said.

The area of Lebanon where the flights took place borders southern Syria.

Israeli violations of Lebanese airspace are not uncommon and Lebanese authorities routinely lodge complaints at the UN against the flights.

Israel captured the Golan Heights from Syria in the 1967 war, and Syria demands the area back as part of any peace deal. Despite hostility between the two countries, Syria has been careful to keep the border quiet since the 1973 Mideast war and has never retaliated to Israeli attacks since.

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.