Libyan opposition leader Moustafa Abdel-Jalil said Thursday that the rebel forces' chief of staff Abdel Fattah Younes was killed.

Head of the rebel forces Abdel Fattah Younes addresses a news conference in Benghazi in this April 5, 2011 file photo. Younes was shot dead by assailants on July 28, 2011 according to Libyan rebel leader Mustafa Abdel Jalil. Younes was killed by assailants after he had been summoned before a judicial committee that was looking into the military operations. [Xinhua/Reuters Photo]

The National Transitional Council (NTC) chairman Jalil told a press conference that supporters of Muammar Gaddafi were responsible for the death of Younes. Two other military leaders were also killed.

The NTC would hold a three-day mourning for the death of Younes, Jalil said in the rebels' stronghold Benghazi.

The Libyan government in Tripoli has not commented on the statement of the NTC.

Younes, Gaddafi's former security minister, defected to the rebel in February, and was leading the rebels' military campaign against Gaddafi.

Reports said Younes was recalled from the front line hours before he was killed, but it was not immediately known why he was recalled.