A powerful explosion rocked a Christian suburb of northern Beirut, residents said.
The mid-morning blast reverberated all over the Lebanese capital.
There were no immediate reports of casualties and it was not clear who was targeted by the explosion.
The blast went off in the neighbourhood of Naqash, a district several miles from the US Embassy compound and from the residence of Christian anti-Syrian leader Michel Aoun.
Earlier, Lebanese television has reported that outgoing deputy prime minister and defence minister Elias Murr was wounded in a bombing north of Beirut.