Lebanese police say a suicide bomber has detonated explosives inside a bus in southern Beirut.
It was not immediately clear if anyone besides the bomber was killed.
Television footage from the scene showed the mangled remains of the vehicle with its roof blown off and body parts scattered across the road.
The target of the attack was not immediately known.
There have been a number of recent suicide bombings in Lebanon, where violence has spilled over from the Syrian conflict. Many of the bombings have targeted strongholds of the Shi'ite militant group Hezbollah, which has sent fighters to Syria to support Syrian government troops.