Benghazi: The commander of the Libyan rebels' military was killed by fellow rebels while in custody after he was arrested by the opposition's leadership on suspicion of treason, witnesses said on Saturday, indicating a potentially major split in the ranks of the movement battling Muammar Gaddafi.

The killing of Abdel-Fattah Younis under still mysterious circumstances raised fear and uncertainty in
Benghazi, the de facto rebel capital, and worries among Western allies who have backed the rebels controlling most of the eastern Libya.

The National Transitional Council, the rebels' leadership body, has said it is investigating the killing. It blamed unidentified "gunmen" and has made no confirmation that Younis had been arrested. It has said only that Younis was gunned down on route to Benghazi, where he had been summoned to discuss "a military matter."

But a rebel special forces officer under Younis' command said that Younis was taken before dawn on Wednesday from his operations room at Zoueitina, just east of the main front with Gahdafi's forces.

Fighters from a rebel faction known as the February 17 Martyr's Brigade came to the operations room and demanded Younis come with them for interrogation, said the officer, Mohammed Agoury, who said he was present at the time.

Agoury said he tried to accompany his commander, "but Younis trusted them and went alone."

"Instead, they betrayed us and killed him," he said. Younis' body was found on Friday, dumped outside Benghazi, along with the bodies of two colonels who were his top aides. They had been shot and their bodies burned.