At least 20 people died and 200 were wounded Thursday when a car packed with explosives was detonated in a mainly Shi'ite Muslim neighborhood of the Lebanese capital.
The attack occurred in South Beirut near Martyrs' Square, which is used by the Shi'ite Hezbollah movement to hold events and meetings.
A dense column of black smoke could be seen rising from the blast site.
Al Manar television, the voice of Hezbollah, said that body parts had been found 10 meters (yards) from the spot where the bomb detonated.
Responsibility for the attack was claimed by the group known as "Aisha the Mother of Believers Brigades for Foreign Missions" in a video posted on Islamist Web pages, but its authenticity has not yet been able to be verified.
Appearing in the video is a masked man who urges Lebanese citizens to stay away from the regions controlled by Hezbollah, since - he claims - additional attacks will occur there.
Thursday's Beirut attack was unanimously condemned by all Lebanese leaders.
President Michel Suleiman said in a communique that the strike was "cowardly, since it sent a message with the blood of innocents."
Meanwhile, outgoing Prime Minister Nayib Mikati condemned the attack and proclaimed Friday as a day of national mourning.
Mikati called for Friday a meeting of the Superior Defense Council at the Baabda presidential palace.
On July 9, a car bomb blew up in the same part of Beirut injuring 53 people.
On Wednesday, Hezbollah leader Hassan Nasrallah claimed responsibility for the explosions that wounded four Israeli soldiers last week in Lebanese territory. EFE