BEIRUT : An explosion tore through a crowded commercial street Thursday in a south Beirut neighborhood that is bastion of support for the Shiite group Hezbollah, killing at least five people, setting cars ablaze and sending a column of black smoke above the Beirut skyline.

The nature of the blast that hit during rush hour in the Haret Hreik neighborhood was not immediately clear, but a Lebanese security official said it appeared to be caused by a car bomb. The official spoke on condition of anonymity because he was not authorized to brief the media.

If confirmed as a bombing, it would be the latest in a wave of attacks to hit Lebanon in recent months as the civil war in Syria increasingly spills over into its smaller neighbor. The violence has targeted both Sunni and Shiite neighborhoods, further stoking sectarian tensions that are already running high as each community in Lebanon lines up with its brethren in Syria on opposing sides of the war.

Lebanon's official National News Agency said at least five people were killed and more than 50 wounded in the explosion, which left the mangled wreckage of cars in the street and blew out the windows of store fronts. The director of the Bahman Hospital, were dozens of the wounded were taken, said many of the injured were in critical condition.

Images from Associated Press television showed firefighters putting out the smoldering hulks of several cars that had been set ablaze. Crowds swarmed around ambulances waiting for the wounded with their lights flashing. At least one building had part of its facade blown off, and several neighboring buildings were also damaged.

Hezbollah's Al-Manar TV said the explosion occurred "a few hundred meters (yards) from the politburo of Hezbollah." It said the political office was not the target of the blast.

"Suddenly, the whole area went bright and we started running away," Ali Oleik, an accountant who works in a nearby office building, told The Associated Press. "I saw two bodies on the street, one of a woman and another of a man on a motorcycle who was totally deformed."

Hezbollah security agents as well as Lebanese troops were trying to cordon off the area to keep the angry crowds away from the blast site. Authorities brought out bomb sniffing dogs, and at one point announced over megaphones that there might be another bomb, setting the panicked crowd scattering.

The explosion comes a week after a car bombing in downtown Beirut killed prominent Sunni politician Mohammed Chatah. The former finance minister and top aide to ex-Prime Minister Saad Hariri was critical of Syrian President Bashar Assad and his Hezbollah allies.

Hezbollah's once seemingly impenetrable bastion of support — Beirut's southern suburbs — also has been hit several times in recent months.

In November, suicide bombers targeted the Iranian Embassy in Beirut, killing at least 23 people. Iran is the chief patron of Hezbollah and an ally of Syria, and the Islamic Republic's embassy is located in a Hezbollah district.

Another blast in August killed around 20 people in the Beir al-Abed district, near the Haret Hreik neighborhood were Thursday's bombing took place.

Two weeks later, a double bombing outside two Sunni mosques in the northern city of Tripoli killed scores more.

The attacks raise the specter of a sharply divided Lebanon being pulled further into the Syrian conflict, which is being fought on increasingly sectarian lines pitting Sunnis against Shiites. Syria-based Sunni rebels and militant Islamist groups fighting to topple Assad have threatened to target Hezbollah strongholds in Lebanon in retaliation for intervening on behalf of his regime in the conflict.

Caretaker Prime Minister Najib Mikati said the targeting of south Beirut area, less than a week after the bombing that killed Chatah "proves that the hand of terrorism does not differentiate between the Lebanese."

"The fire burning in more than one region of Lebanon portends what is worse if we do not meet and deal with our problems away from the language of defiance and exclusion," he said in a statement.

HP