A large explosion hit a Hezbollah stronghold in south Beirut Thursday, the Shiite group's Al-Manar television reported, on the heels of a November double suicide bombing at Iran's embassy in the area.

"A very big blast hit Haret Hreik... targeting an area that is very densely populated," Al-Manar said in an initial report.

Ambulance sirens were heard in the capital. Al-Manar showed footage of emergency vehicles arriving at the scene.

The broadcaster also aired pictures of bystanders scrambling to put out fires in cars parked beneath a building whose facade was badly damaged by the explosion.