Gaddafi said his withdrawal from his Bab al-Aziziya headquarters in the heart of the capital was a tactical move after it had been hit by 64 NATO air strikes and he vowed "martyrdom" or victory in his fight against the alliance.

As night fell on Tuesday after a day in which rebels overran Tripoli, meeting little resistance with few casualties, heavy fighting was reported in a southern desert city, Sabha, that rebels forecast would be Gaddafi loyalists' last redoubt.

Forces loyal to Gaddafi were shelling the towns of Zuara and Ajelat west of Tripoli, Al-Arabiya television reported.

In Tripoli itself, Reuters correspondents said there still appeared to be some hostile fire around the city center as darkness descended and looting broke out.

Al-Arabiya quoted a witness as saying that loyalist forces had fired dozens of Grad missiles at the city.

The continued shooting suggested the six-month popular insurgency against Gaddafi, a maverick Arab nationalist who defied the West and kept an iron hand on his oil-exporting, country for four decades, had not completely triumphed yet.

A spokesman for Gaddafi said the Libyan leader was ready to resist the rebels for months, or even years.