“We have issued a code of ethics in handling of prisoners of war,” The NTC vice chairman Abdel Hafiz Ghoga said.

“I am sure that was an individual act and not an act of revolutionaries or the national army. Whoever is responsible for that [the killing) will be judged and given a fair trial.”

The final moments of the deposed leader are still shrouded in mystery.

He was pulled alive from a drain as he tried to escape his hometown of Sirte but a video later shows him bleeding and being pushed against a truck.

A post-mortem revealed he was killed by a single gunshot to the head and had also been shot in the stomach. There is no footage of his actual death – yet.

Originally the NTC claimed Gaddafi had been killed in crossfire between rebels and pro-Gaddafi troops.

But there have been renewed calls for an investigation as footage published in the US suggests Gaddafi was sexually assaulted shortly before his death.

Gaddafi’s family meanwhile have reportedly said they will sue NATO for “war crime charges” in an international court.

Marcel Ceccaldi, the Gaddafi family lawyer, apparently told a French radio station: “The relatives of the late dictator will file a suit on war crime charges. NATO helicopters opened fire on Gaddafi’s convoy…This convoy did not pose any threat to civilians. It was an operation to eliminate the Libyan leader, planned by the North Atlantic alliance.”

NATO is expected to end its mission in Libya, seven months after it began, now that Gaddafi’s oppressive 42-year rule is kaput.