An explosion rocked a stronghold of the Shiite Hezbollah group in the southern suburbs of the Lebanese capital, killing at least five people, setting cars ablaze and sending a column of black smoke above the Beirut skyline.
The nature of the explosion 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.
If confirmed as a bombing, then 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 attacks have targeted both Sunni and Shiite neighborhoods, further stoking sectarian tensions that are already running high because of the war next door.
Lebanon's Health Ministry said at least five people were killed and 20 wounded in the explosion, which left the mangled wreckage of cars in the street and blew out the windows of store fronts.
Images broadcast on Hezbollah's Al-Manar TV showed firefighters putting out the smoldering hulks of several cars that had been set ablaze. The footage showed at least one building that had part of its facade blown off, and several neighboring buildings were also damaged.
Al-Manar 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.
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.
"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."
Authorities brought out bomb sniffing dogs, and at one point announced that there might be another bomb, setting the crowd scattering in panic from the area.
The explosion comes a week after a car bombing in downtown Beirut killed a prominent Sunni politician who had been 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.
The Haret Hreik neighborhood where Thursday's explosion took place is close to the Beir al-Abed district where a powerful car bomb in August killed nearly 20 people.
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.