Pro-government militias battled fighters in a former stronghold of the late Libyan dictator Muammar Gaddafi, the fifth straight day of clashes that have killed at least 30 people.
The fighting in Bani Walid, some 90 miles south east of Tripoli, has overlapped with the anniversary of Gaddafi's capture and killing on October 20, 2011.
A year since his death brought an end to Libya's civil war, Bani Walid is the most significant city in the country to still resist the nation's new authorities.
A resident said by telephone that pro-government militias and fighters in the city were clashing on its outskirts. The resident said there were reports of new casualties, but that the fighting was less intense than a day earlier.
In Tripoli, some two hundred protesters demonstrated in front of the parliament building to urge the end of the fighting, which they say is harming only civilians. The demonstration was dispersed by a massive show of force when army units pulled up and opened fire above the heads of the crowd with heavy weaponry.
Government forces near Bani Walid said there were no civilians in the conflict area, and they had helped evacuate hundreds of residents a day earlier.
The official Lana news agency said at least 22 pro-government militiamen were killed during clashes. Pro-government militiamen said most of the casualties came during an ambush by fighters in the besieged city.
A spokesperson for UN Secretary-General Ban Ki-moon said in a statement on Sunday that Mr Ban was alarmed by the growing number of civilian casualties and calling on Libyan authorities and those in Bani Walid to begin resolving the stand-off peacefully.
The violence coincided with conflicting reports about whether security forces had arrested Gaddafi's former spokesman, Moussa Ibrahim, in Bani Walid.
The government said its forces had apprehended Mr Ibrahim, but never produced evidence to support its statement. Then an audio recording purportedly by Mr Ibrahim surfaced on the internet denying that he had been arrested or that he was even in Libya.