Seven people, including Lebanon's former finance minister, Mohamad Chatah, have been killed in a car bombing in central Beirut.
Friday's blast in the capital struck close to the government's headquarters and parliament, injuring at least 71 people, according to initial medical reports.
Immediate footage showed people fleeing the area of the incident in the residential Ain el-Merasa district, with cars ablaze and people on fire, as clouds of black smoke billowed over surrounding banks, restaurants and hotels.
Six people were killed on Friday. The seventh, 16-year-old Mohammed Chaar, died of his wounds the next morning.
Al Jazeera's Rula Amin, reporting from the site of the attack, said the blast was so strong that even people in nearby buildings were injured as windows shattered.
Medics and army troops were deployed to the scene where Chatah was believed to have been targeted as his convoy was passing through.
Former Prime Minister Saad Hariri and his March 14 coalition accused Lebanon's Shia Hezbollah group and Syria, of involvement in the killing of Chatah, Hariri's 62-year-old political adviser.
"This is a terrible loss for Lebanon, the Lebanese people and for the United States.
"As far as we are concerned the suspects ... are those who are fleeing international justice and refusing to represent themselves before the international tribunal," Hariri said.
Chatah's killing occurred three weeks before the long-delayed opening of a trial of five Hezbollah suspects indicted for the 2005 bombing which killed former Prime Minister Rafik Hariri, Saad's father, and 21 other people.
The trial is due to open in The Hague in January.
The suspects are all fugitives and Hezbollah, which denies any role in the Hariri assassination, has refused to cooperate with the court, which it says is politically motivated. Preliminary UN investigations implicated Syrian officials.
Chatah was a vocal critic of Syrian President Bashar al-Assad's regime in Syria as well as Hezbollah, which has sent fighters to Syria to prop up regime forces.
A message on his Twitter account less than an hour before the blast accused the group of trying to take control of the country.
"Hezbollah is pressing hard to be granted similar powers in security and foreign policy matters that Syria exercised in Lebanon for 15 years," the tweet read.
Damascus rejected accusations that it was behind the blast.
"These wrong and arbitrary accusations are made in a context of political hatred," said Syria's Information Minister Omran al-Zohbi, in remarks published by state news agency SANA.
Hezbollah condemned the attack, calling it a "terrorist explosion".
"The despicable crime is part of a series of crimes that aim to destroy Lebanon," the statement, carried by the group's al-Manar TV, said.
The conflict in Syria has polarised Lebanon and increased sectarian tensions. Hezbollah has sent fighters to Syria to fight alongside Assad, who is from the Alawite sect, an offshoot of Shia Islam.
US Secretary of State John Kerry said, "this is a terrible loss for Lebanon, the Lebanese people and for the United States."
United Nations Secretary-General Ban Ki-moon condemned the bomb attack, and the 15-member Security Council expressed its "unequivocal condemnation of any attempt to destabilise Lebanon through political assassinations."
Mohammed Chaar, the seventh person killed in the attack, was lying on the pavement, his head bloodied, before he was taken to hospital with severe injuries.
Chaar had been identified online as one of four youths seen posing in a group selfie posted on social media networks in front of the car that exploded moments later.
The picture went viral on the internet, and the confirmation of his death sparked an outpouring of tributes on social media websites like Facebook and Twitter on Saturday.