The fighters, who are still trying to exert their control over the entire country nearly three weeks after storming into the capital, revealed in Tripoli that they had arrested the head of the ousted leader's external spy service.
Gaddafi himself remains on the run and a handful of towns in Libya remain under the control of his followers. Fighters for the interim National Transitional Council had given holdout towns a deadline of Saturday to surrender, and have been fighting since Friday inside the town of Bani Walid.
They said on Sunday they were meeting stiff resistance in the town 150km southeast of the capital and were also edging towards the ousted ruler's birthplace Sirte.
"We are inside Bani Walid, we control big chunks of the city. There are still pockets of resistance," one fighter named Sabhil Warfalli said as he drove away from the front line in the town.
NTC spokesman Ahmed Bani told reporters the plan for Bani Walid for now was to wait.
"When our forces entered Bani Walid they found the brigades of Gaddafi using citizens as shields," he told reporters. "We entered to prove that we can, and saw with our own eyes, Grad missiles over the roofs and they were using civilians."
"There are houses full of families and they are just standing outside that house, and also missiles over that house, so we are unable to strike the house because we know there are civilians inside. Also NATO can do nothing. So we prefer to return and surround Bani Walid until the young men inside have a solution," he said.
Inside the capital, Reuters reporters saw Bouzaid Dorda, a former prime minister who ran Gaddafi's external spy service, held by a group of about 20 fighters under guard in a house in the capital's Zenata district.
Dorda will be handed over to Libya's interim governing council later on Sunday, an anti-Gaddafi fighter said.
A tall, lanky figure in safari jacket and slip-on shoes, Dorda was sitting on a sofa and was not physically restrained but an armed guard sat beside him. He declined a request for an interview, but in response to an assertion by a fighter that he had killed people, he replied: "Prove it."
"I am innocent until proven guilty. I am willing to be referred to the Libyan prosecutor general," he said. Visibly agitated, he added: "You have to remember it was a regime already in existence."
Warfalli, the fighter outside Bani Walid, said pro-Gaddafi forces were now concentrated in the central market area -- an account backed up by a resident named Khalifa Telisi who had telephoned a family in the town.
"There is still resistance from the central market. All other parts of Bani Walid have been liberated," Telisi said.
Inside the town, a pro-Gaddafi local radio station appealed for the city's 100,000 people to fight to the death.
"We urge the people of Bani Walid to defend the city against the rats and armed gangs. Don't back down. Fight to the death. We are waiting for you. You are just a bunch of gangsters. God is on our side," an announcer said. The language echoed turns of phrase used by Gaddafi in recent broadcasts.
Jalil al-Galal, an NTC spokesman in Tripoli, said resistance from Gaddafi fighters firing rockets and mortars inside the town had been "ferocious". Nevertheless, NTC spokesman Bani predicted council forces would have total control of Libya by the end of this month.
Gaddafi's loyalists also control Sirte, which sits on the main east-west coastal highway, effectively cutting Libya in two. Advancing NTC troops said the front line was now about 90 km east of the city.
Fighters were firing tanks and howitzers amid the sound of heavy machinegun fire and the roar of NATO warplanes overhead.
"There were clashes this morning and Gaddafi forces were firing Grad rockets, but we managed to advance a little bit and we will enter Sirte very soon," fighter Salah al-Shaery said.
NTC chairman Mustafa Abdel Jalil, a former Gaddafi justice minister who has run the council from the eastern city of Benghazi, arrived in Tripoli on Saturday for the first time since bands of anti-Gaddafi rebels captured it on August 23.
"Brotherhood and warmth -- that's what we will depend on to build our future. We are not at a time of retribution," Abdel Jalil declared. "This is the time of unity and liberation."
The NTC has said it will complete its move to Tripoli this week, although previous timelines for this have slipped.
Establishing a credible interim government in the capital would mark an important step for Libya, where regional and factional rivalries among forces united only by contempt for Gaddafi could plague efforts to reshape the country.
The NTC also promised to resume oil production, virtually stalled since the civil war began six months ago, within days.
But Abdel Jalil said it was still too early to declare Libya "liberated" from the man who ruled it for 42 years.
"Gaddafi still has money and gold," he said. "These are the fundamental things that will allow him to find men."
