Eight people have been killed and more than 78 injured after a massive car bomb tore through a middle-class largely Christian neighbourhood of Beirut.
One of the dead – apparently the target of the attack – was a senior internal security official, Major General Wissam al-Hassan. Hassan had been behind the break up of an alleged pro-Syrian network that had been smuggling explosives into Lebanon for a bombing campaign.
The death of Hassan, who reportedly had concerns he had become a target for assassination, is bound to lead to speculation that Syria, or its allies were behind the attack despite the quick condemnation by Damascus of the attack.
Confirming his death, a senior Lebanese intelligence official told Reuters: "I can just say that it is true, he is dead."
News of his death was also reported by Lebanese media outlets quoting security sources.
Hassan also led the investigation that implicated Syria and its ally Hezbollah in the killing of the former prime minister Rafik al-Hariri a Lebanese, official said.
With Lebanon already destabilised by the war in neighbouring Syria, the assassination of Hassan will heighten the danger of a return to sectarian violence.
As head of the police intelligence unit, he was a prime mover behind the arrest earlier this year of Michel Samaha, a pro-Syrian former information minister and close ally to President Bahar al-Assad. Samaha is said to have confessed to smuggling explosives into Lebanon to launch a bombing campaign in the country's north.
The car bomb attack in Beirut follows fresh evidence that the conflict in Syria is spreading beyond its borders and threatening to draw in neighbouring countries into a wider conflict, including Turkey and Syria. Earlier on Friday it was reported that Syrian forces had ambushed and killed 17 Lebanese close to the countries joint border.
The Beirut blast was immediately condemned by Hariri's son Saad, also a former prime minister.
"The cowardly terrorist attack in Ashrafieh today is an attack on all of Lebanon and all Lebanese," Hariri said, whose father was killed in a similar car bomb attack. "This was a cowardly act aimed at destabilising Lebanon and its security."
The blast damaged buildings in a six-block radius and was audible across a large part of the city, sending up a pall of black smoke above the skyline.
In the immediate aftermath of the blast the Lebanese Red Cross and civil defence officials released conflicting totals for the number killed.
The bomb, which struck a city that has become increasingly tense due to the frictions of the neighbouring war in Syria, hit the well to do Ashrafieh neighbourhood.
Body parts were scattered at the scene, while emergency workers evacuated the injured – including children – some by motorbike. As the scale of the bombing became clear, local hospitals appealed for blood donors.
The engine of the car carrying the bomb was thrown from the scene, while neighbouring buildings were heavily damaged.
The blast occurred in the middle of rush hour, also when many parents were picking up children from school, in the street where the office of the anti-Damascus Christian Phalange party is located near Sassine Square.
The party's leader, Sami al-Gemayel, a staunch opponent of Assad and member of Lebanese parliament, condemned the attack.
"Let the state protect the citizens. We will not accept any procrastination in this matter, we cannot continue like that. We have been warning for a year. Enough," said Gemayel, whose brother was assassinated in November 2006.
The war in Syria has pitted mostly Sunni insurgents against Assad, who is from the Alawite sect linked to Shia Islam.
Tension between Sunnis and Shias has been simmering in Lebanon ever since the end of the 1975-1990 civil war and have reignited amid the Syria conflict.
Tensions peaked when Hariri, a Sunni, was killed in 2005. His supporters accused Syria and then Hezbollah of killing him, a charge both deny. An international tribunal accused several Hezbollah members of involvement in the murder.
The group's political opponents, who have for months accused it of aiding Assad's forces, have warned that its involvement in Syria could reignite sectarian tension in Lebanon.
The last bombing in Beirut occurred in 2008 when three people were killed in an explosion which damaged a US diplomatic car.
However, fighting had broken out this year between pro- and anti-Assad factions in the northern Lebanese city of Tripoli.