Libyan opposition leader Moustafa Abdel-Jalil said Thursday that the rebel forces' chief of staff Abdel Fattah Younes was killed, according to a report by Xinhua news agency.

The National Transitional Council (NTC) chairman, Jalil, told a press conference that supporters of Muammar Gaddafi were responsible for the death of Younes> However Al Jazeera reported Younes had been arrested and "was being held at an undisclosed military garrison in Benghazi."

"The reason behind the former minister of interior's arrest on Thursday has not been made public."

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

There has been speculation that some of the opposition fighters did not trust Younes because of his previous role as Gaddafi's security minister. Younes had defected to the opposition in February.

Jalil told journalists two other military leaders were also killed. The NTC would have three days of mourning for the death of Younes, Jalil said.

The Libyan government has not commented on the statement by the NTC.