A huge car bomb has killed at least eight people and injured 78 in central Beirut, Lebanese officials say.
The explosion occurred in a busy street in the predominantly Christian district of Ashrafiya.
The intended target may have been top intelligence official Wissam al-Hassan, officials say. Some reports say he was killed.
No group has said it carried out the bombing. Tensions in Lebanon have been rising over the conflict in Syria.
Mr Hassan was involved in the uncovering of a recent bomb plot that led to the arrest of a pro-Syrian Lebanese politician.
Friday's attack was the deadliest in Beirut since 2008. It took place near Sassine Square, at a time when many parents were picking up children from school.
Hospitals across the city have reported large numbers of wounded, and called for people to donate blood.
The blast caused considerable damage, setting cars ablaze and destroying the facades of nearby buildings.
Ronnie Chatah, who lives 500m from the site of the blast, told the BBC: "The building shook and it echoed throughout the neighbourhood."
Lebanese Prime Minister Najib Mikati said the government was trying to identify the perpetrators and said they would be punished.
The attack occurred close to the headquarters of the Kataeb, better known as the Phalange, a Maronite Christian group.
The general secretariat of the Western-backed 14 March coalition of former Prime Minister Saad Hariri is also based in the area.
An MP from the alliance, Michel Pharaon, told al-Jazeera TV: "I think Ashrafiya is a target, and 14 March is a target. This region is symbolic because it is in the heart of the capital and it is a Christian neighbourhood."
Some 14 March politicians have specifically accused the Syrian government of being behind the bombing.
However Syrian Information Minister Omran al-Zoubi called it a "cowardly terrorist act".