Lebanese security officials at the scene of the bomb blast
Anti-Syrian politicians in Lebanon have accused Damascus of being behind a powerful car bomb that killed the head of Lebanon's internal intelligence.
Opposition leader Saad Hariri and Druze leader Walid Jumblatt both said Syrian President Bashar al-Assad was behind the bombing in Beirut. A Syrian minister condemned the blast.
Hariri's coalition called on the government to resign, reports the BBC.
Friday's blast left eight people dead and wounded dozens.
It occurred in the mainly Christian district of Ashrafiya, in a busy street close to the headquarters of Saad Hariri's 14 March coalition.
Internal intelligence head Wissam al-Hassan was among those who died. He was close to Hariri, a leading critic of the government in neighbouring Syria.
Hassan led an investigation that implicated Damascus in the 2005 bombing that killed Hariri's father, former Prime Minister Rafik Hariri.
He also recently organised the arrest of a former minister accused of planning a Syrian-sponsored bombing campaign in Lebanon.
Lebanon's religious communities are divided between those who support the government of Syrian President Bashar al-Assad - including many Shias - and those mostly from the Sunni community who back the rebels.
Tension in Lebanon has been rising as a result of the Syrian conflict.
"We accuse Bashar al-Assad of the assassination of Wissam al-Hassam, the guarantor of the security of the Lebanese," Hariri said on Lebanese TV.
Jumblatt told satellite channel Al-Arabiya: "[Bashar al-Assad] is telling us that even though he turned Syria into rubble, `I am ready to kill in any place"'.
Nadim Gemayel, an MP from the right-wing Christian Phalange Party, also pointed to Syria, where an uprising against Assad that began 18 months ago has led to an increasingly violent conflict.
"This regime, which is crumbling, is trying to export its conflict to Lebanon," he said.
Hariri's March 14 bloc issued a statement accusing the Beirut government of protecting "criminals" and calling on it to stand down.
Anti-Syrian protesters burned tires during demonstrations in Beirut and Tripoli late on Friday.
The force of Friday's blast, the worst in the Lebanese capital for four years, ripped balconies from the fronts of buildings and set many cars on fire. For many, it evoked scenes from Lebanon's civil war in the late 1970s and 1980s.
Lebanese Prime Minister Najib Mikati said the government was trying to identify the perpetrators and they would be punished.
Lebanon's Shia militant group Hezbollah - a close ally of the Syrian government - condemned the bombing.
Syrian Information Minister Omran al-Zoubi called it a "cowardly, terrorist act". He said such incidents were "unjustifiable wherever they occur".
UN Secretary General Ban Ki-moon called on "all Lebanese parties not to be provoked by this heinous terrorist act", while EU foreign policy chief, Catherine Ashton called on "all Lebanese to remain calm".
US Secretary of State Hillary Clinton called the bombing a "dangerous sign that there are those who continue to seek to undermine Lebanon's stability."
"Lebanon must close the chapter of its past and bring an end to impunity for political assassinations and other politically motivated violence," she said.