Columns of military vehicles of Libya's provisional government advanced on the Muammar Gaddafi stronghold of Sirte on Saturday as NATO planes roared overhead, Reuters reports.
Explosions were heard inside the town, which, along with the desert town Bani Walid is a last remaining bastion of support for the deposed leader.
Forces of the ruling National Transitional Council were seen advancing from both the west and the south of Sirte.
At the western gate, gunners fired artillery towards the town. Both sides exchanged volleys of rockets and NATO jets flew overhead. Large plumes of black smoke rose from inside the town.
The rebel forces have previously retreated from Sirte, Gaddafi's hometown, and Bani Walid after poorly organised assaults met fierce resistance from Gaddafi loyalists.
A man in Libya who esaped from Sirte says the situation is very serious for civilians there.
