At least five people have been killed and more than 60 hurt in a car bomb which hit a suburb of Lebanon's capital Beirut, media and officials say.
The blast destroyed several vehicles and part of the facade of a building in a densely populated area of Haret Hreik district.
The southern suburb is a stronghold of the Shia militant group Hezbollah.
Beirut has recently been hit by attacks linked to heightened Sunni-Shia tensions over the Syrian war.
Former minister Mohamad Chatah, a Sunni and a critic of Hezbollah, was killed by a car bomb last Friday. Six other people died and at least 50 were injured.
Former Prime Minister Saad Hariri, to whom Mr Chatah was an adviser, blamed Hezbollah for that attack but it has denied any involvement.
Hezbollah's TV station Al-Manar showed large crowds gathered around twisted and burnt-out vehicles in front of a building that had been badly damaged in Thursday's blast.
Lebanese military officials said the bomb was detonated in a four-wheel-drive vehicle.
Human remains in addition to the five confirmed dead were found near the car, suggesting a suicide attack, security sources said.
The street is home to shops, restaurants and residential buildings. The TV said the explosion took place a few hundred metres from the nearest Hezbollah political offices.
"Suddenly, the whole area went bright and we started running away," Ali Oleik, an accountant working in a nearby building, told the Associated Press news agency.
The UN Security Council issued a statement condemning the bombing, calling for national unity and urging all Lebanese parties "to respect Lebanon's policy of disassociation and to refrain from any involvement in the Syrian crisis".
Hezbollah has sent fighters to Syria to help President Assad in the war against Sunni-led rebels there. President Assad comes from the Alawite sect, an offshoot of Shia Islam, while many Lebanese Sunnis sympathise with the Syrian rebels.
Lebanese politicians also spoke out against the bombing.
Mr Hariri described it as a "diabolical act", while caretaker Prime Minister Najob Mikati said terrorists "were planning a despicable conspiracy to drown the Lebanese in sectarian strife".
Hezbollah deputy leader Sheikh Naim Qassem called for calm, and for the formation of a new government.
"Lebanon is on the road to ruin if there is no political understanding," he told al-Manar.
Lebanon has been without a government since the resignation of Mr Mikati's administration in April 2013.
BBC Arab affairs editor Sebastian Usher says the bomb is not one of the biggest of the recent incidents, but that its impact was considerable because it was detonated during rush hour.
No-one has yet said they carried out the attack. It came a day after the reported arrest of Majid al-Majid, the head of a Sunni jihadist group which claimed a suicide bomb attack on the Iranian embassy in Beirut in November.
That attack, in the same part of the city as Thursday's bomb, left 23 people dead.
Majid al-Majid, the Saudi "emir" of the al-Qaeda-linked Abdullah Azzam Brigades, had said that attacks would continue in Lebanon until Iranian and Hezbollah forces stopped fighting alongside government forces in Syria.
Earlier in December, a senior Hezbollah commander with close links to Iran, Hassan Lakkis, was shot dead outside his home near Beirut.