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 Gaddafi 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-Gaddafi 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 an interview with The Daily Telegraph, Anders Fogh Rasmussen, the Nato Secretary General, said that Islamic extremists would "try to exploit" any weaknesses created as Libya tried to rebuild.
In a new report released Tuesday, Amnesty International accused Gaddafi'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 Gaddafi'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.
Gaddafi, 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.