Interim leader Mustafa Abdel Jalil received a hero's welcome when he made a public speech in Tripoli's main
square late on Monday.
Thousands celebrated last month's fall of the Kadhafi regime in Martyrs' Square, two days after Abdel Jalil, the head of the National Transitional Council (NTC), arrived in Tripoli from Benghazi in the east.
Moderate Islam would be the main source of legislation in post-Kadhafi Libya, he told the crowd.
"We will not accept any extremist ideology, on the right or the left. We are a Muslim people, for a moderate Islam, and we will stay on this road," he said.
In a new report released Tuesday, Amnesty International accused Kadhafi's regime of crimes against humanity but also said NTC fighters had committed possible war crimes.
While the London-based rights group's report consisted mainly of damning examples of violations by Kadhafi's regime, it said the NTC appeared unwilling to hold its fighters accountable for human rights violations.
Amnesty said in the first days of the uprising against Kadhafi's rule groups of protesters killed a number of captured soldiers and suspected mercenaries.
"Some were beaten to death, at least three were hanged, and others were shot dead after they had been captured or had surrendered, the report, "The Battle for Libya -- Killings, Disappearances and Torture," said.
"The NTC is facing a difficult task of reigning in opposition fighters and vigilante groups responsible for serious human rights abuses, including possible war crimes but has shown unwillingness to hold them accountable," the report said.
Kadhafi, meanwhile, in a statement read out on Syria-based Arrai Oruba television, vowed to defeat those behind the "coup" that ousted him.
"It is not possible to give Libya to the colonialists again," the one-time strongman said.
"All that remains for us is the struggle until victory and the defeat of the coup," added the former leader who has gone underground since Tripoli fell to rebel fighters late last month.
On the battlefield, Kadhafi's remaining forces launched ferocious counterattacks Monday on the oil refinery town of Ras Lanuf in the east, on the road towards Kadhafi's hometown of Sirte, and at Bani Walid southeast of the capital Tripoli.
Striking deep behind enemy lines, Kadhafi fighters killed at least 12 NTC soldiers at Ras Lanuf, an NTC military spokesman told AFP.
The oil infrastructure along the Mediterranean coast between Sidra and Brega was a key battleground of the seven-month uprising against Kadhafi, as the mainly rebel-held east and mainly government-held west fought it out.
But since Tripoli's fall, NTC forces have advanced dozens of kilometres (miles) west towards Sirte, which remains in Kadhafi's hand, moving to secure the vital oil infrastructure on which its post-war reconstruction plans depend.
Southeast of Tripoli, civilians poured out of the desert town of Bani Walid Monday after intense fighting between Kadhafi loyalists and troops of the new regime who have encircled it.
But those fleeing said many more remained trapped inside the oasis town, 180 kilometres (110 miles) from the capital, for want of fuel for their vehicles.
"Families are scared to death by this war," said Mohammed Suleiman as he passed through a checkpoint with 10 relatives crammed into the back of his white BMW.
West of Sirte, an NTC commander said his forces had met strong resistance as they advanced to a place called "Checkpoint 50" -- 50 kilometres from the town.
"We came under fire from a lot of Grads (rockets)," said field commander Umran al-Awaib.
The unexpected counter-offensive by Kadhafi loyalists came despite the flight to neighbouring Niger of 32 members of his inner circle during the past 10 days.
"A total of 32 people are now here, including one of (Kadhafi's) sons, Saadi, as well as three generals," Niger's Prime Minister Brigi Rafini said.
They crossed the border in four separate groups and had been taken in for "humanitarian reasons", he added.
The most recent arrivals included Saadi, the third of Kadhafi's seven sons, who has a reputation as a playboy; and eight of the fallen despot's other close associates, Rafini added.
US State Department spokeswoman Victoria Nuland said Niger was preparing to detain Saadi.
"We have confirmed with the government of Niger that Saadi crossed over, that they are either in the process or have already brought him to the capital of Niamey and intend to detain him," she said.
On the diplomatic front, China which opposed the NATO campaign backing the anti-Kadhafi forces, finally recognised Libya's interim government after weeks of holding back.
Washington also announced it had sent an advance team to help its officials reopen the US embassy in Tripoli.