Libya's new rulers promised to investigate allegations of "serious abuses" including war crimes as their position was consolidated when the World Bank recognised them as the official government.
The National Transitional Council was responding to a report released Tuesday by London-based human rights watchdog Amnesty International that accused the fighters who brought down the Kadhafi regime.
The NTC acknowledged "a small number of incidents involving those opposed to Kadhafi" and vowed to investigate Amnesty's allegations.
Amnesty said in the first days of the uprising groups of anti-Kadhafi 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," Amnesty said.
"The NTC is facing a difficult task of reining in opposition fighters and vigilante groups responsible for serious human rights abuses, including possible war crimes, but has shown unwillingness to hold them accountable," it said.
But Amnesty acknowledged the alleged atrocities were of a "smaller scale" than those carried out by Kadhafi's regime, which it says may be responsible for crimes against humanity.
In a statement issued in its eastern bastion of Benghazi, the council's executive committee said it "strongly condemns any abuses perpetrated by either side".
"The NTC is firmly committed to human rights and the rule of law, both international and local," it said.
In his first public speech since arriving in Tripoli on Saturday, Libya's interim leader Mustafa Abdel Jalil told thousands of supporters in Martyrs' Square that moderate Islam would be Libya's main source of legislation.
"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 Monday night.
The World Bank said its decision was based on "evolving events in Libya and the views of member countries."
It pledged a major rebuilding role after the seven-month insurrection that ousted the fugitive Kadhafi.
The NTC meanwhile continued to seek the surrender of Kadhafi diehards who have been mounting attacks against its fighters from a few enclaves, including the oasis town of Bani Walid, southeast of Tripoli.
Kadhafi, wanted for crimes against humanity by the International Criminal Court, remains in hiding.
Earlier, in a statement read out on Syria-based Arrai Oruba television, he vowed to defeat those behind the "coup" that had ousted him.
"All that remains for us is the struggle until victory and the defeat of the coup," he said.
NATO said it did not know if Kadhafi senior was still in Libya.
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"He has not made public appearances in the country for a while and this raises questions about his whereabouts," spokesman Colonel Roland Lavoie told reporters from the operation's headquarters in Naples, Italy.
Thirty-two members of Kadhafi's inner circle, including his son Saadi, have fled to Niger.
Saadi Kadhafi arrived in the Niger capital Niamey late Tuesday under the protection of the country's security forces, a Nigerien government source said.
He flew in from the northern town of Agadez on a Hercules c-130 transport plane, local sources said.
In Agadez, he had stayed at the governor's residence with eight other close associates of his father, they added.
The International Energy Agency said Libya could recover a quarter of its oil production by the end of 2011, and two-thirds by end-2012.
A return to full output of about 1.6 million barrels a day could take two to three years, it said.
Canada said it has freed up $2.2 billion of Libyan assets frozen in its banks as it renewed ties with the North African country.
The World Bank's recognition of the NTC came a day after China, which had long helped prop up Kadhafi before the uprising broke out, became the last permanent member of the UN Security Council to do so.
But South African President Jacob Zuma said the African Union still did not recognise Libya's new leaders.
On the battlefield, fighters of Libya's new rulers brandished new weapons outside Bani Walid, where residents were fleeing fearing clashes with Kadhafi forces.
Talks were under way through mediators for the surrender of Kadhafi diehards but "so far there is no result," said Abdullah Kenshil, the NTC's chief negotiator.
"They want to continue to fight and yesterday they bombed residential areas," he said.
Kenshil, citing fleeing residents, said the humanitarian situation in Bani Walid was difficult, with shortages of water, electricity and commodities.
Although a deadline set for Kadhafi loyalists to surrender has expired, the NTC assault on the desert town 180 kilometres (110 miles) southeast of Tripoli has been stalled for three days.
The area was mainly calm Tuesday, save for intermittent exchanges of fire and the sound of NATO warplanes flying overhead.
NATO said its warplanes had hit a radar system, eight surface-to-air missile systems, five surface-to-air missile trailers, an armed vehicle and two air defence command vehicles.
Those strikes came a day after Kadhafi loyalists launched ferocious counterattacks on the oil refinery town of Ras Lanuf in the east and on the road towards Kadhafi's hometown of Sirte.