Burned-out vehicles blocked roads Monday as provisional government tanks and artillery pounded pro-Gadhafi positions that NTC fighters said were squeezed into two neighborhoods.
On Sunday, National Transitional Council fighters in Sirte took three important landmarks - the city's main hospital, the university and the Ouagadougou convention center that Gadhafi loyalists had used as their main base of operation.
Most NTC forces attacking Sirte are from other towns, putting them at a distinct disadvantage against the remnants of Mr. Gadhafi's army who know the city well. Many civilians from Sirte also are fighting alongside loyalist fighters.
In the southern city of Bani Walid, the other remaining pro-Gadhafi bastion, revolutionary fighters retreated from the town center after facing heavy sniper fire and booby-traps, but they still hold the airport and two nearby villages.
NTC officials say the capture of Sirte will allow them to declare the country liberated, because it will mean the provisional government controls all of the country's ports and harbors.
Sirte is 360 kilometers east of Libya's capital, Tripoli, and has served as a center of support for Mr. Gadhafi. Anti-Gadhafi fighters have been trying to move into the city for three weeks.
Also Monday, an NTC official said he believes Mr. Gadhafi is hiding in the southwestern desert near the borders with Niger and Algeria.
Moussa al-Kouni, a minority Tuareg representative on the council, provided no evidence for his claim. He also denied that ethnic Tuaregs are protecting the fugitive leader.
Some military officials have alleged that members of the nomadic community are helping Mr. Gadhafi survive. The group inhabits the desert border of Niger, Mali, Libya, Algeria and Chad and has long been among the former leader's strongest supporters. Many Tuaregs fought for Mr. Gadhafi during the civil war.