JERUSALEM - Israel accused Iran and Syria on Thursday of sending weapons to Lebanon's Hezbollah in violation of UN resolutions, after one of the militant group's weapons depots blew up near the Israeli border.

Israel, which fought a fierce but inconclusive monthlong war with Hezbollah in 2006, has long charged that the Islamic group is rearming and preparing for another round of fighting.

Hezbollah, which is both a powerful political party and a guerrilla movement, is backed by both Syria and Iran. The conditions of the 2006 cease-fire that ended the Israel-Hezbollah war prohibit weapons smuggling to Hezbollah and forbid the group from engaging in military activities in south Lebanon.

Hezbollah's political influence has burgeoned since the war, and according to Israel and Hezbollah itself, so has its military might -- adding to growing regional alarm over the power of its major patron, Iran.

A senior Israeli officer told reporters the warehouse that blew up on Tuesday in southern Lebanon contained active, short-range rockets that were smuggled from Syria. The Israeli military, he said, had aerial pictures of the site after the explosion.

"The walls of the building were crushed and there are also many holes in the roof of the building," he said, speaking on condition of anonymity under military regulations. "We believe that this is one of dozens of ammunition storage (depots) in southern Lebanon that were built by Hezbollah." This particular depot is part of "the buildup of the Hezbollah force" in Lebanon, he added.

Hezbollah has not commented on the explosion in the village of Khirbet Silim, 15 kilometres north of Israel's border.

Israeli government spokesman Mark Regev said the incident was evidence of "Iranian and Syrian efforts to continue to transfer weapons to Hezbollah in direct and flagrant violation" of the 2006 cease-fire.

Under the truce, a 13,300-member UN peacekeeping force was deployed along Lebanon's border with Israel to help 15,000 Lebanese government troops extend their authority into the south for the first time in decades and create a buffer zone free of Hezbollah fighters.

Lebanese officials said Tuesday's explosions in a supposedly abandoned building were caused by a fire in a Hezbollah weapons storage facility within the buffer zone. The UN peacekeeping force called the incident a "serious violation" of the cease-fire, and the Lebanese army and UN peacekeepers cordoned off the blast area.

Hezbollah leader Hassan Nasrallah has said his group has replenished its stock since the war and possesses more than 30,000 rockets. Hezbollah is also suspected of possessing anti-aircraft missiles -- a suspicion cemented after a Lebanese military helicopter was shot at last year as it flew over Hezbollah mountain bases.

In March 2008, UN Secretary-General Ban Ki-moon cited Israeli claims that Hezbollah commanded 10,000 long-range rockets and 20,000 shorter-range ones. Other Israeli officials have said the number is much higher, and that the range of some of the projectiles has quadrupled since the 2006 war to 300 kilometres.

Before the 2006 conflict, Israel estimates, Hezbollah had 14,000 rockets. Nearly 4,000 rockets bombarded Israel during the war.

Israel also claims that Hezbollah possesses hundreds of anti-tank and anti-aircraft missiles, and that the bulk of the group's weapons reach Lebanon through its porous border with Syria.

Ban has called on Hezbollah to disarm and demobilize and has expressed alarm at Hezbollah's public admission that it provided arms to the militant Palestinian Hamas group that controls the Gaza Strip.

Israel's Foreign Ministry said Thursday it was weighing an official complaint to the UN about Tuesday's incident.

Hezbollah won support at home and in the Arab world for fighting Israel to a draw in the 2006 war, which killed about 1,200 Lebanese and 160 Israelis.

It parlayed that backing into expanded political might that peaked after its gunmen overran pro-government neighbourhoods in the Lebanese capital, Beirut, last year. The violence allowed Hezbollah lawmakers to wrest a reconciliation agreement that gave the group and its opposition allies veto power in the government.

Although a Western-backed coalition defeated Hezbollah in June elections, the group and its allies are demanding veto power in the next unity government that Premier-designate Saad Hariri is attempting to form.

There is also growing evidence of Hezbollah's fingerprints across the Mideast. In April, Egypt accused Hezbollah of organizing a cell to carry out terror attacks inside Egypt.