Libyan rebels appear to have "summarily executed" scores of fighters loyal to Moammar Gadhafi, and probably the dictator himself, when they overran his hometown a year ago, a human rights group said Wednesday.

The report by Human Rights Watch on alleged rebel abuses that followed the October 2011 capture of the city of Sirte in the final major battle of the eight-month civil war is one of the most detailed descriptions of what the group says were war crimes committed by the militias that toppled Gadhafi, and which still play a major role in Libyan politics today.

The 50-page report, titled "Death of a Dictator: Bloody Vengeance in Sirte," details the last hours of Gadhafi's life on Oct. 20, 2011, when he tried to flee the besieged city. The longtime leader's convoy was struck by NATO aircraft as it tried to escape and the survivors were attacked by militias from the city of Misrata, who captured and disarmed the dictator and his entourage.

Moammar Gadhafi is shown surrounded by Libyan fighters in Sirte, Libya, in a video from the day he died. (APTN/Associated Press)

Misrata was subjected to a brutal weeks-long siege by Gadhafi's forces that killed hundreds of residents, and fighters from the city became among the regime's most implacable foes. HRW says it seems the Misratans took revenge against their prisoners in Sirte.

"The evidence suggests that opposition militias summarily executed at least 66 captured members of Gadhafi's convoy in Sirte," said Peter Bouckaert, emergencies director at Human Rights Watch.

The New York-based group's report says that new evidence unearthed in its investigation includes a mobile phone video clip taken by militiamen showing a large number of prisoners from Gadhafi's convoy being cursed and abused by rebels.

The remains of at least 17 of the detainees in the phone video were later identified in a group of 66 bodies found at Sirte's Mahari hotel, some still with their hands tied behind their back. Human Rights Watch said it used hospital morgue photos to confirm the victims' identities.

The dictator himself was seen alive in a widely-circulated video made public shortly after the battle.

"Video footage shows that Moammar Gadhafi was captured alive but bleeding heavily from a head wound," the HRW report says. But footage showed that he was "severely beaten by opposition forces, stabbed with bayonet in his buttocks, causing more injuries, and bleeding. By the time he is filmed being loaded into an ambulance half-naked, he appears lifeless."

Gadhafi son's body also found in morgue

Bouckaert said the group's "findings call into question the assertion by Libyan authorities that Moammar Gadhafi was killed in crossfire and not after his capture."

Gadhafi's son Muatassim was also videotaped alive and in captivity, only to have his body turn up at a morgue in Misrata alongside his father's.

"In case after case we investigated, the individuals had been videotaped alive by the opposition fighters who held them and then found dead hours later," Bouckaert said. "Our strongest evidence for these executions comes from the footage filmed by the opposition forces and the physical evidence at the Mahari hotel where the 66 bodies were found."

Another victim cited by HRW as an example was 29-year-old Ahmed al-Gharyani, a navy recruit from the town of Tawergha. He was seen alive in the phone video as rebels beat him. His body was later found in the hotel and eventually identified by his family.

His hometown, Tawergha, was used as a staging ground by Gadhafi's forces to launch attacks on Misrata, but after rebels broke the siege on Misrata and overran Tawergha, the town's residents fled or were driven out by vengeful rebels.

Suleiman al-Fortia, a member of the dissolved National Transitional Council from Misrata, denied that Gadhafi or his loyalists were executed. "We hoped to arrest Gadhafi alive (to try him). All the killings took place in a crossfire," he said.

But HRW said that "under the laws of war, the killing of captured combatants is a war crime, and Libyan civilian and military authorities have an obligation to investigate war crimes and other violations of international humanitarian law."

The group released its report days before Libya celebrates "liberation day," the anniversary of Sirte's fall on Oct. 23.

Since then, the country's new leaders have heavily depended on former rebel militias to secure cities and protect borders in the absence of a strong national army or other government security forces.

Calls for militias to be brought under the control of the defence or interior ministries have met resistance from some fighters.