One of those killed in the attack was identified as Maj. Gen. Wissam al-Hassan, a top official of the Internal Security Forces, The Washington Post reported. Hassan was an ally of Sunni leader and former Prime Minister Saad Hariri, the newspaper said.
Mohammed Chatah, an adviser to Hariri, said the death of Hassan -- whose investigation found evidence Hezbollah was involved in the 2005 assassination of former Prime Minister Rafiq Hariri -- "is a big, big, big event, and one cannot begin even to think through the repercussions."
Nadim Gemayel, a Christian member of Parliament, said the car bomb attack was "a political one for sure. It aimed to create terror and start a civil war in the country."
Health Minister Ali Hasan Khalil said the death toll from the explosion -- which rocked the largely Christian area of the city near Sassine Square around 2:50 p.m., the time workers and students in the area would be commuting home -- would likely rise.
The explosion tore through a narrow street lined with apartment buildings, near the headquarters of the right-wing Kataeb Party and the anti-Syrian "March 14" coalition of parties, the Beirut Daily Star reported.
The cause of the explosion was a car rigged with dynamite, Lebanese Army explosives experts said after a preliminary examination.
March 14 coalition Secretary-General Fares Souied blamed embattled Syrian President Bashar Assad for the blast, calling it an "act of terror" and noting to the MTV Lebanon television channel Assad had repeatedly "threatened to set fire to the region if the noose tightened on him."
Syria said in a statement aired on a media outlet allied with Hezbollah, "The criminal behind the explosion is not yet known, and the party responsible is hidden in the chaos of the political struggle in the country."
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