Muammar Gaddafi's besieged hometown of Sirte was rocked by heavy street fighting on Friday, as the ex-leader called on Libyans to turn out in their millions to demonstrate against the country's new rulers.
An AFP correspondent said there were particularly violent clashes around and inside the university, near the city centre.
Street fighting and heavy bombardment also continued from overnight at the Ouagadougou conference centre, a major stronghold of pro-Gaddafi forces, while the Mauritanian Quarter was also under attack.
Meanwhile, medics at a field hospital 50 kilometres (35 miles) west of Sirte said 18 injured anti-Gaddafi fighters had been brought in, most of them with shrapnel wounds, but that there were no immediate reports of any killed.
Gaddafi made his call late Thursday on Syria-based Arrai television, as the National Transitional Council's forces pressed their three-week campaign to capture Sirte.
"I call on the Libyan people, men and women, to go out into the squares and the streets and in all the cities in their millions" to reject the NTC, the deposed leader said in a scratchy audio message.
"I say to them, do not fear anyone. You are the people, you belong to this land," said Gaddafi, whose whereabouts are unknown but is widely thought to still be in Libya.
"Make your voice heard against NATO's collaborators," he said, in reference to the new regime.
Fighting on Sirte's northeastern front had erupted Thursday morning after Gaddafi diehards advanced under the cover of darkness, fighters told AFP.
Sirte and Bani Walid, a desert town 170 kilometres (100 miles) southeast of of Tripoli, are Gaddafi's last major bastions against the NTC, which has ruled most of the oil-rich country since the veteran strongman was toppled in August.
By midday Thursday, NTC fighters had halted the pro-Gaddafi assault and were advancing on foot among the buildings, in the face of rocket and sniper fire.
Thursday night, the Ali Nuri Sbag Brigade advanced nearly a kilometre (0.6 mile), bringing them close to the north-south thoroughfare that forms a pro-Gaddafi stronghold, an AFP correspondent said.
The brigade is made up mostly of defectors from Gaddafi's army. Their professionalism is evident, in marked contrast to the amateurism of certain units of civilian volunteers.
Defenders had erected a sand berm to block the main road, so the attackers had to navigate a maze of alleys, two-storey homes and gardens.
The narrow lanes made it almost impossible for military vehicles to move forward without being targeted by snipers, forcing Mismari's men to proceed on foot, guns at the ready.
Meanwhile, NTC reinforcements were sent to Bani Walid for another assault of Gaddafi's loyalists who are fiercely defending the oasis.
Mussa Ali Yunes, commander of the Jado Brigade, said "we are heading for the southern front of Bani Walid," speaking of a column of 1,000 men and hundreds of vehicles.
Yunes said efforts were being made to convince the remaining 10 percent of the population still there to leave before the new assault is launched after a month-long siege.
"The offensive could, possibly, be launched in two days, but that depends" on the situation, he added, explaining that the NTC forces were outgunned.
"There are many weapons in Bani Walid, weapons of high technology, very recent, coming from Russia," he said. "We need more precise weapons but also intelligence on the inside, particularly on the number of missiles they have.
"About 2,000 fighters are deployed on the northern front, but they only have light weapons for now, because all the heavy weapons are in Sirte."
Yunes said Gaddafi son "Seif al-Islam is in Bani Walid and possibly Gaddafi as well, but there is a 50 percent doubt about that. There are many Gaddafi loyalists in Bani Walid, more than in Sirte."
On Tuesday, an NTC commander said Seif al-Islam was leading the final stand inside the besieged oasis.
Seif al-Islam, his father and Gaddafi's intelligence chief Abdullah al-Senussi are the subject of International Criminal Court war crimes arrest warrants for murder and persecution in the bloody uprising.