The rush-hour blast in the Lebanese capital, Beirut, yesterday killed eight people and wounded about 80 others, heightening fears that Syria's civil war is spilling over into Lebanon.
Among the dead was Wissam al-Hassan, the head of a Lebanese intelligence agency who had also uncovered a recent bomb plot that led to the arrest of a pro-Syrian Lebanese politician.
Mr al-Hassan was a close aide to Hariri, a Sunni Muslim who was killed in a 2005 bomb attack in Beirut. Al-Hassan's investigation into Hariri's death uncovered evidence that implicated Syria and Hezbollah in the killing.
Yesterday's bombing, reminiscent of grim scenes from Lebanon's own 1975-1990 civil war, was seen as being linked to the heightened tension between Lebanese factions on opposite sides of the conflict in Syria.
The explosion ripped through the street where the office of the anti-Damascus Christian Phalange Party is located near Sassine Square in Ashrafiyeh, a mostly Christian area.
Several cars were destroyed and the front of a multi-storey building was badly damaged, with tangled wires and metal railings crashing to the ground.