A prominent Lebanese security official is among the dead in a car bombing in the capital Beirut that has killed eight people and wounded at least 96 others.
Wissam al-Hassan, intelligence chief of the Internal Security Forces (ISF), was the brain behind uncovering a recent bomb plot that led to the arrest of Michel Samaha, a Lebanese politician close to Syrian President Bashar al-Assad, who has been accused of trying to help smuggle explosives into Lebanon.
The ISF was also deeply involved in seeking the arrest of those responsible for a host of attacks and assassinations between 2005 and 2008, starting with the murder of Rafik al-Hariri.
Following the attack, clashes occurred in the northern city of Tripoli between the rival districts of Jabal Mohsen and Bab al-Tabbaneh, leaving one person dead. Jabal Mohsen is mainly populated by mostly Alawites supportive of Assad, while Bab al-Tabbaneh is a Sunni area.
Friday's rush-hour car bombing has raised fears of renewed sectarian violence in a country still scarred from a long civil war. Hassan was seen as close to Saad al-Hariri, leader of the opposition March 14 alliance and a son of the slain former prime minister.
Al Jazeera's Rula Amin, reporting from Beirut, said: "Wissam al-Hassan was a very prominent figure in Lebanon.
"He played a key role in pursuing the killers of Rafik al-Hariri, and one of his most recent achievements is the capturing and arrest of Michel Samaha.
"He is a very controversial figure for the March 8 alliance. He was a key figure in supporting the armed opposition in Syria, and the March 14 alliance is going to take this explosion much more seriously.
"This killing will stir a lot of tensions."
When asked who he thought was responsible for the killing, Saad al-Hariri replied: "Bashar Hafez al-Assad. Who killed Wissam al-Hassan is as clear as day. Certainly the Lebanese people will not be silent over this heinous crime and I, Saad Hariri, promise that I will not be silent."
The Lebanese government said on Friday that an investigation has been launched into the assassination of Hassan.
Calls for PM resignation
But the opposition called on the government to resign following an emergency meeting. "The government must leave and we call on Prime Minister Najib Mikati to resign immediately," said Ahmad al-Hariri, secretary-general of Saad Hariri's Future movement.
The explosion occurred at a time of heightened tension between Lebanese factions on opposite sides of the conflict in neighbouring Syria.
Ambulances rushed to the scene of the blast in the Ashrafiyeh district, a mostly Christian neighbourhood, as smoke rose from the area.
The explosion struck a street where the office of the Christian Phalange Party is located, near Sassine Square.
Phalange leader Sami al-Gemayel, a staunch opponent of Assad and a member of Lebanon's 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.
Our correspondent said that already there were fears that the bombing meant the Syrian crisis had spilled over into Lebanon.
Lakhdar Brahimi, the UN-Arab League peace envoy to Syria, "warned two days ago that you cannot expect the Syrian crisis to remain within Syrian borders", she said.
Syria condemned the deadly car bombing, describing it as "a cowardly terrorist act", state news agency SANA reported.
Omran al-Zohbi, Syrian information minister, was quoted as saying "these sort of terrorist, cowardly attacks are unjustifiable wherever they occur".
Meanwhile, the 15-member UN Security Council, in a statement, called the attack a "heinous act" and appealed to the Lebanese people to "preserve national unity in the face of such attempts to undermine the country's stability."
The US said the bombing was a "terrorist attack".
"There is no justification for using assassination as a political tool," National Security Council spokesman Tommy Vietor said in a statement.
Ziad Baroud, a former Lebanese interior minister, told Al Jazeera that it was too soon to tell who was behind the deadly car bombing.
"High-ranking officials have not said anything so far, and therefore neither can I," he said.
"We have no indication whatsoever [of who is behind this]. We know this is a strong and sad message, and we know this could destabilise the whole country."
|Omar Nashabe of Al Akhbar daily and Nadim Badran, a resident of Ashrafiyeh, discuss Friday's bombing in Beirut
Michel Pharaon, a Lebanese politician with the March 14 alliance, told Al Jazeera that the coalition may have been a target of the explosion.
"We have had lately some assassination attempts, which has reminded us of the period between 2005 and 2007, and this terrorist act is also a reminder of what used to happen in Ashrafiyeh during these years," he said.
Several cars were set on fire by Friday's explosion and the front of a multistorey building was badly damaged.
Residents ran about in panic looking for relatives while others helped carry the wounded to ambulances.
Security forces were quickly deployed in large numbers in the area.
Nadim Badran, a resident of Ashrafiyeh, told Al Jazeera his entire building shook when the explosion occurred.
"I quickly made my way to the scene of the blast, and I saw glass on the street, people running, people screaming," he said.
"This is the first time since I've been living here for the last 20 years that I have felt like a sitting target. This is a message to all of us, that we are all targets. It could happen to any of us."
Regarding the possible consequences, Badran said: "As Lebanese we have absolutely no faith, no trust, no belief that anyone who did this can be found and brought to justice."
The most prominent car bombing since Lebanon's 1975-1990 civil war took place on February 14, 2005, when a massive blast killed Rafik al-Hariri and 22 other people as his motorcade drove along the Beirut waterfront.