A powerful car bomb exploded in central Beirut on October 19, killing at least eight people and wounding about 80.
Lebanese state-run media said a senior intelligence official, Wissam al-Hassan, was among those killed.
The motive for the bombing was not immediately clear, but the explosion came amid growing concerns that the conflict in neighboring Syria could spill over into Lebanon.
Health Minister Ali Hassan Khalil, speaking at the scene of the explosion, said the bombing was a "terrorist act" aimed at destabilizing Lebanon.
"We have always said that Lebanon should be distanced from what is going on in the region now and our policy was to avoid getting into that mess as much as possible," he said. "But unfortunately, this act is a terrorist act aimed at destabilizing the security of the Lebanese.''
Lebanese political factions and religious communities are divided over Syria's conflict. Some support Syrian President Bashar al-Assad's regime, while others back the rebels who are fighting against Assad's rule.
The conflict in Syria pits mostly Sunni Muslim rebels against Assad's regime, which is dominated by members of the Alawite community -- an offshoot of Shi'ite Islam.
The October 19 blast occurred in predominantly Christian east Beirut, near the headquarters of the Christian Phalange party. The Phalange party opposes Assad.
The security official who was killed, Hassan, had led an investigation that implicated Syria and Lebanon's Hizballah Shi'ite militia in the killing of former Prime Minister Rafik al-Hariri. Both have denied any involvement.
Hariri, a Sunni Muslim, was killed by a 2005 car bomb attack in Beirut.
Hassan also led an investigation that uncovered a recent bombing plot that led to the arrest of a Lebanese politician who is allied with Assad.
Rafik Hariri's son, former Lebanese Prime Minister Saad Hariri, has accused the Syrian president of being behind the killing of Hassan.
U.S. State Department spokeswoman Victoria Nuland condemned the bombing in Beirut, calling it an "act of terrorism." The bombing also was condemned by the Vatican, while French President Francois Hollande called on Lebanese politicians to remain united and prevent attempts to destabilize the country. The UN Security Council also "strongly condemned the terrorist attack."
Syria has for a long time played a major role in Lebanese politics, particular during Lebanon's 1975-90 civil war. Syrian troops occupied parts of the country during that war and remained in Lebanon until 2005.
With reporting by dpa, AP, and AFP