BEIRUT - A powerful car bomb struck the southern Beirut stronghold of Lebanon's militant Hezbollah group on Thursday, killing 20 people, wounding 120 and trapping many others inside damaged buildings, witnesses and emergency officials said.
The blast, a month after another car bomb wounded more than 50 people in the same district of the Lebanese capital, came amid sectarian tensions over the intervention of Shi'ite Muslim Hezbollah against Sunni rebels in Syria's civil war.
A Sunni Islamist group calling itself the Brigades of Aisha claimed responsibility for the attack and promised more operations against Hezbollah. It was not immediately possible to verify the statement, made in an Internet video.
"I don't know what happened. It's as if we were struck by an earthquake," one young man at the scene told Reuters, bleeding from a wound to his stomach.
At the heart of the site, where fires raged an hour after the blast, the twisted remains of a large van could be seen.
Many cars were engulfed in flames, the charred bodies of drivers or passengers still visible inside. The blast sent a column of black smoke over the densely populated area and the facades of several residential buildings were damaged.
Al Mayadeen television said some people were trapped inside apartments at the scene, close to the Sayyed al-Shuhadaa (Martyrs) complex, where Hezbollah leader Sayyed Hassan Nasrallah often addresses his followers.
Residents of southern Beirut say Hezbollah, backed by Iran and Syria, had been on high alert and stepped up security in the area after warnings from Syrian rebels of possible retaliation for the group's support for President Bashar al-Assad.
"I heard a huge explosion. It threw me several meters," said a woman in her 50s who said she had been talking to her brother in his shop. "I don't know what happened to my brother. I can't find him," she said, bleeding from wounds to hands and face.
"This is the second time that we decide the time and place of the battle ... And you will see more, God willing," the Brigades of Aisha statement said, describing Hezbollah and Nasrallah as Iranian agents.
"We send a message to our brothers in Lebanon, we ask you to stay away from all the Iranian colonies in Lebanon ... because your blood is precious to us," a masked spokesman, flanked by two men brandishing rifles, said in the video.
"But Hassan Nasrallah is an agent of Iran and Israel and we promise him more and more (attacks)."
There have been two previous attacks in southern Beirut this year, as Syria's conflagration seeps across the border into Lebanon. Two months before the July 9 car bomb, two rockets were fired into the area.
Sectarian violence fuelled by the Syrian conflict has also erupted in the Bekaa Valley and the Mediterranean port cities of Tripoli and Sidon, reflecting the renewed sectarian tension spreading through the Middle East.
Lebanon's Sunni Muslims mostly support the rebels in Syria, while Shi'ites have largely supported Assad, who is part of the minority Alawite sect, an offshoot of Shi'ite Islam.
Hezbollah leader Nasrallah has promised that his group will continue fighting for Assad after it spearheaded the recapture of the strategic town of Qusair in June.
In October last year, a car bomb in the east of the capital killed a senior intelligence official, Wissam al-Hassan, who was close to the country's leading Sunni opposition party, which has supported the uprising in Syria.