Sixteen people have died after a powerful car bomb struck the southern Beirut stronghold of Lebanon's militant Hezbollah group.
Over 200 people were wounded in the blast and many others were trapped inside damaged buildings.
The blast came amid sectarian tensions over the intervention of Shia Muslim Hezbollah against Sunni rebels in Syria's civil war.
A Sunni Islamist group calling itself the Brigades of Aisha claimed responsibility for the attack and promised more operations against Hezbollah.
It was not immediately possible to verify the statement, made in an internet video.
Health Minister Ali Hassan Khalil said hospitals across the capital admitted a total of 16 bodies and 226 wounded people.
At the heart of the site, where fires raged an hour after the blast, the twisted remains of a large van could be seen.
Many cars were engulfed in flames, the charred bodies of drivers and passengers still visible inside.
The blast sent a column of black smoke above the densely populated area and the facades of several residential buildings were damaged.
Al Mayadeen television said some people were trapped inside apartments at the scene, close to the Sayyed al-Shuhadaa (Martyrs) complex, where Hezbollah leader Sayyed Hassan Nasrallah often addresses his followers.
Residents of southern Beirut say Hezbollah, backed by Iran and Syria, had been on high alert and stepped up security in the area after warnings from Syrian rebels of possible retaliation for the group's support for President Bashar al-Assad.
In a statement, the Brigades of Aisha said: "This is the second time that we decide the time and place of the battle ... And you will see more, God willing."
However, many Lebanese politicians pointed the blame at Israel.
Interior Minister Marwan Charbel said: "The explosion was carefully prepared and one of the theories is that it could have been an Israeli retaliation for the Labouneh operation."
He was referring to an incident last week when four Israeli soldiers were wounded in southern Lebanon.
Caretaker Prime Minister Najib Mikati declared tomorrow would be a day of mourning for the victims of the blast.
