Human Rights Watch says it has new evidence indicating that forces opposed to Moammar Gadhafi beat and executed dozens of his supporters after the ousted leader's capture and death last year.
Gadhafi died on October 20, 2011, after his convoy of supporters trying to flee the city of Sirte was hit by an airstrike and attacked by militia members.
The report, issued Wednesday, says militias subjected detainees from Gadhafi's convoy to brutal beatings and later executed 66 of them at a nearby hotel.
Human Rights Watch's Peter Bouckaert said the event should be considered a war crime and prosecuted as such.
"We should not forget that more than 66 people in his convoy, who just happened to be part of the people fleeing from Sirte, were taken away and very brutally abused," he said. "We have videos taken by the rebels themselves showing them beating, cursing and spitting upon these captured persons – and then they were executed. So it's a very significant war crime and should be prosecuted as such."
Human Rights Watch says it used the videos and hospital morgue photos to link at least 17 detainees to the bodies found at the hotel.
The group says its findings also call into question the conclusion of Libyan officials that Gadhafi was killed in crossfire between loyalist fighters and provisional government forces. It says Gadhafi and his son Mutassim were alive in video taken after their capture, and later found dead.
Human Rights Watch raised questions about the circumstances of Gadhafi's death last October and called on Libyan authorities to investigate a possible mass execution of his supporters during the battle for Sirte. The group said Wednesday that it has seen no evidence that an inquiry is under way or has been carried out.
The new report is based on videos taken by opposition forces and interviews with surviving members of Gadhafi's convoy.
Libya's new government has been trying to gain control of militias, which have grown stronger since Gadhafi's fall. National Assembly President Mohammed el-Magarief vowed last month to dissolve all militias and military camps operating outside the control of the government.