The death toll from Thursday’s car bombing in the southern Beirut stronghold of Hezbollah rose Friday to 24, said Ali Ammar, an MP for the Lebanese Hezbollah group.

Lebanon’s health minister, Ali Hassan Khalil, said earlier 21 bodies were taken to hospitals and another 335 people had been treated for their injuries, Reuters reported.

A previously unknown group said it carried out Thursday ' s attack in the densely populated southern suburbs of Beirut, between Bir al - Abed and Rweiss, districts where Hezbollah security is normally tight.

The National News Agency reported that seven people, including a man and his three children, were missing.

On Friday morning, investigators were combing the scene for clues, as Hezbollah security personnel sealed off the area. Group members in civilian clothes stopped and searched cars in the southern suburbs.

The explosion, reminiscent of the frequent attacks during Lebanon ' s 1975-1990 civil war, sent a plume of black smoke into the Mediterranean sky, caused heavy damage to buildings and set several cars ablaze.

Leaders from across the political spectrum condemned the bombing, and a day of mourning was declared.

President Michel Sleiman said the " terrorist " bombing targeted all Lebanese, not just Hezbollah.

Former prime minister Saad Hariri, said the attack was " part of a vicious terrorist scheme " targeting Lebanon.

UN chief Ban Ki - moon urged Lebanon ' s fractious political scene to stay united, in a statement that condemned the bombing as " completely unacceptable ".

" During this period of heightened tensions, the secretary general urges all Lebanese to remain united, to rally around their state institutions and to focus on safeguarding Lebanon ' s security and stability, " the statement said.