A blast has rocked a densely populated neighborhood of south Beirut, killing at least five people in an area known as a Hezbollah stronghold.
Thursday's explosion wounded about 20 people. Hezbollah's Al-Manar television showed ambulances racing to the scene and burning wreckage.
The nature of the blast is still unclear, but Lebanese Health Minister Ali Hassan Khalil told reporters the government was fighting a "battle against terrorism."
Television footage showed a charred automobile covered with leaves and rubble falling from balconies of nearby buildings.
The explosion comes less than a week after a massive car bombing in central Beirut killed former Lebanese finance minister Mohamad Chatah, a harsh critic of Syrian President Bashar al-Assad.
Five other people were killed and about 70 wounded in that blast.