BEIRUT -- Gunmen assassinated a senior Hezbollah commander after he parked his car in his apartment building's garage Wednesday in Lebanon's capital, a major breach of the Shiite militant group's security as it struggles to maintain multiple fronts while it fights alongside President Bashar Assad's forces in Syria.

The killing of Hassan al-Laqis, 53, was the latest in a series of attacks against the Iranian-backed group whose heavy-handed and very open involvement in the civil war next door has enraged the overwhelmingly Sunni rebels seeking to oust Assad and fueled sectarian tensions across the region.

The militant group quickly blamed its main enemy Israel, which has a history of taking out Hezbollah leaders but denied any responsibility. Suspicion also fell on Sunni rivals who have claimed responsibility for recent deadly car bombings in Hezbollah strongholds and a double suicide attack targeting the Iranian Embassy in Beirut last month.

Al-Laqis' killing came shortly after Hezbollah leader Sheik Hassan Nasrallah accused Saudi Arabia of being behind the embassy bombings, which killed 23 people, in a three-hour interview with a local television station. Nasrallah indirectly suggested an alliance between Israel and Saudi Arabia was trying to destabilize the group.

The killing and other attacks underscored how the Shiite militia has found itself mired into fronts: Shoring up Assad's rule in Syria, and against the Jewish state. Hezbollah's fight in Syria marked a strategic shift for the fiercely anti-Israel group, one that some of its most loyal supporters in the Shiite community have been reluctant to embrace.

It has emboldened the group's critics in the Arab world and its Western-backed political opponents in Lebanon who blame it for dragging Lebanon into Syria's war, which pits the mainly Sunni rebels against Assad, who belongs to the Alawite sect, a Shiite offshoot.

The fighting has stoked Lebanon's Sunni-Shiite tensions, as each community in Lebanon lines up in support of its brethren on the rival sides in Syria. That has fueled predictions that the country, still recovering from its 15-year civil war that ended in 1990, is on the brink of collapsing into full-blown sectarian bloodletting of its own.

In Lebanon's second-largest city, Tripoli, bloody street battles between rival sides has become a near-daily affair, with at least 12 people killed over three days last week.

Al-Laqis, described as a founding member of the group, was killed as he returned home from work about midnight, Hezbollah said in a statement.

"The brother martyr Hassan al-Laqis, spent his youth and all his life in this honourable resistance since its inception up until the last moments of his life," it said.

An official close to Hezbollah said al-Laqis held some of the group's most sensitive portfolios and was very close to Nasrallah and his inner circle.

The parking lot was stained with muddied footprints that led to a small olive grove nearby. Yellow police tape blocked off the area and Hezbollah investigators were at the scene.

A Lebanese security official and the official close to Hezbollah said several gunmen appear to have been involved in the assassination, but al-Laqis was shot with a pistol equipped with a silencer at close range after he parked his car in the ground floor garage of his apartment building in the Hadath neighbourhood, just southwest of Beirut.

He was struck by five bullets in the head and neck, the Lebanese official said. The gunmen fled, and al-Laqis was rushed to a nearby hospital but died early Wednesday of his wounds, officials said, speaking on condition of anonymity because they weren't authorized to release the information before a formal announcement.

"I was trying to sleep, and I heard ... a bullet being fired and a dog barking," said Abdullah, a local resident who wished to be identified only with his first name for security reasons. "I did not bother myself, but later I heard people screaming. I had a look and found it was crowded, and then our neighbours told us that one of the neighbours was assassinated," Abdullah said.

Hezbollah distributed a photograph of al-Laqis and said Israel had tried to kill him several times in the past. The image showed a man with neatly cut black hair and a greying close-cropped beard, wearing beige-and-khaki military clothing.

Al-Laqis was buried later Thursday in his hometown of Baalbek in eastern Lebanon. A few thousand people took part under pouring rain, and women wept as Hezbollah pallbearers carried the coffin, wrapped in the group's yellow flag, through the streets of Baalbek. Hezbollah fighters fired in the air in mourning.

"The Israeli enemy is naturally directly to blame," the Hezbollah statement said. "This enemy must shoulder complete responsibility and repercussions for this heinous crime and its repeated targeting of leaders and cadres of the resistance."

Israeli Foreign Ministry spokesman Yigal Palmor denied any involvement.

"Israel has nothing to do with this incident," Palmor said. "These automatic accusations are an innate reflex with Hezbollah. They don't need evidence, they don't need facts, they just blame anything on Israel."

Hezbollah has fought several wars against Israel. Al-Laqis' son, Ali, died fighting Israel in the monthlong 2006 war. Israel's spy service has been suspected of assassinating Hezbollah commanders for more than two decades.

In 1992, Israeli helicopter gunships ambushed the motorcade of Hezbollah leader Sheik Abbas Musawi, killing him, his wife, 5-year-old son and four bodyguards. Eight years earlier, Hezbollah leader Sheik Ragheb Harb was gunned down in south Lebanon.

But one of the biggest blows for the group came in 2008 when Imad Mughniyeh, a top Hezbollah military commander, was killed by a bomb that ripped through his car in Damascus. Hezbollah and its primary patron, Iran, have blamed Israel's Mossad for the killing.

Associated Press writer Tia Goldenberg in Jerusalem contributed to this report.