A human rights group is urging Libya's provisional authority to end arbitrary detentions and “widespread abuse” of detainees, saying there is a risk of repeating patterns of former leader Moammar Gadhafi's rule.

In a report released Thursday, London-based Amnesty International said it found a pattern of beatings and ill-treatment of pro-Gadhafi soldiers, suspected loyalists and alleged mercenaries in western Libya.

The group said its findings are based on interviews of about 300 prisoners during August and September.

Amnesty International is calling on the National Transitional Council to allow those being held to challenge their detentions or be released. The group said the NTC has acknowledged its concerns and promised to ensure that detainees receive equal protection under the law.

In Libya Wednesday, the NTC issued conflicting statements about whether Mr. Gadhafi's son Mutassim has been arrested in the coastal city of Sirte.

Some NTC officials said Mutassim Gadhafi was captured and taken to the eastern city of Benghazi for questioning. Reuters news agency quoted Mohammed Bouker of the NTC's National Working Group as saying that “an important figure” was arrested and that his name will be released Thursday.

But a spokesman for the provisional government's military council was not able to confirm the reports. Jalal el-Gallal said revolutionary forces did capture some fighters believed to be with Mutassim in Sirte, but that he had no information regarding the status of Mr. Gadhafi's son.

News of the arrest prompted heavy celebratory gunfire in several Libyan cities, including Tripoli and Benghazi. Mutassim was Libya's national security adviser and had a strong role in the military and security forces under his father's government.

There have been false reports regarding the capture of senior Gadhafi figures in the past, including that of another son, Saif al-Islam, who is still on the run.

Earlier Wednesday, revolutionary fighters said they now control more than 80 percent of Sirte, Mr. Gadhafi's hometown, but are still facing stiff resistance from loyalists there.

Revolutionary forces have made significant recent advances in Sirte, seizing the town's police headquarters on Tuesday. Days earlier, the fighters gained control of the main hospital, the university and the convention center that Gadhafi loyalists had used as their main base of operation.

NTC officials have said the capture of Sirte will allow them to declare the country liberated, because it will mean the provisional government controls all of Libya's ports and harbors.

Sirte is 360 kilometers east of Libya's capital, Tripoli, and has served as a center of support for Mr. Gadhafi. Provisional government forces have been trying to take the town for three weeks.