Heavy and sustained gunfire has broken out across the Libyan capital Tripoli.
Residents say there have been clashes between troops still loyal to the country's leader, Muammar Gaddafi and rebel forces.
The official Libyan government position is that this is celebratory shooting in response to pro-Gaddafi troops retaking the key oil port of Ras Lanuf.
According to state television the cities of Zawiya, Misrata and Ras Lanuf are now in government control.
It says troops are heading towards the rebel held city of Benghazi in the east.
But the BBC reports that this can not be independently verified.
There have been protests against Colonel Gaddafi's rule in Tripoli but the city has so far remained under his control.
Many deaths in Zawiya
There has been fierce fighting in the Libyan city of Zawiya, west of the capital Tripoli, with unconfirmed accounts describing a massacre with up to 30 people killed.
Reports from the coastal city said it had come under attack from both east and west from well-armed government forces in large numbers of tanks and armoured vehicles.
Pro-government tanks had circled the area in preparation for the fresh attack, shelling central areas of the city, where fires burned under a cloud of dense black smoke.
Pro-government forces were pushed out of the city centre in heavy fighting on Saturday morning, but regrouped for a fresh assault.
A doctor in Zawiya said at least 30 people had died in Saturday's fighting.
Gaddafi's opponents meet in Benghazi
Colonel Gaddafi's opponents have been meeting in the rebel-controlled eastern Libyan city of Benghazi to consolidate their parallel government, known as the interim National Council.
The man leading the group, the former justice minister, Mustafa Abdel Jalil, says the Council is now Libya's sole legitimate representative.
Mr Abdel Jalil says his group is in contact with European and Arab countries and is expecting international recognition.
The United States says it is boosting international efforts to repatriate thousands of foreign nationals fleeing the unrest.
The State Department says it is contributing about $4 million to the operation coordinated by the International Organisation for Migration.
More than 100,000 refugees have crossed into Tunisia so far.