Air strikes hit the Libyan capital Tripoli early today.

The sound of a jet plane, followed by an explosion at 1am local time sent up a huge cloud of white smoke.

The explosion appeared to have taken place near Bab al-Aziziyah, the sprawling compound of Libyan leader Muammar Gaddafi.

At least two more rumbling blasts could be heard in the east of the city.

Libyan television said an "imperialist Crusader" bombardment had struck the neighbourhood of Ain Zara, in south-east Tripoli.

Under a United Nations mandate, Nato warplanes have been carrying out air strikes on the Libyan government military targets.

A Libyan opposition group, Free Generation Movement, posted online that there were four explosions in the Ain Zara area and speculated the target could have been the External Security headquarters or facilities for storing weapons.

Just 24 hours earlier there were a series of at least six explosions in the Bab al-Aziziyah area. Nato later reported a "command and control" facility had been hit.