Libyan state TV has broadcast an audio message from Colonel Gaddafi, calling on Libyan people around the country to come to Tripoli to free it from the rebels.
It comes as rebels appear to have made key gains as they close in on the capital, where new fighting has been reported.
Witnesses say rebels have taken control of the Tajoura district to the east of the city, and an important military base to the west, enabling them to seize weapons and ammunition.
Dozens of anti-Gaddafi prisoners are reported to have been freed from a jail nearby.
One rebel commander says it is hoped that Tripoli will fall by Monday. Colonel Gaddafi’s former right-hand man, who is now in Rome after defecting, says it might take up to 10 days.
But rebel forces, aided by NATO strikes, have met fierce resistance, having to retreat at least once.
In Tripoli the regime called for a ceasefire, warning of dire consequences otherwise.
“We believe unless the international community heeds this appeal, many people will be killed and terrible crimes will be committed inside several Libyan cities,” Information Minister Moussa Ibrahim told a news conference.
The rebels are ecstatic after making major headway on the road to Tripoli in recent days.
But the government is warning that the capital itself will be resolutely defended.