The Libyan rebels' military commander, Abdel-Fattah Younis, has been killed, the transitional leadership council in Benghazi says.

Update at 5:13 p.m. ET: Younis and his two aides, Col. Muhammad Khamis and Nasir al-Madhkur, were gunned down before they arrived for questioning about suspicions that he and his family still had dealings with Gadhafi's regime, the head of rebel council, Mustafa Abdul-Jalil, said at a news conference. The details still have not been revealed.

The head of the group believed responsible for the killings has been arrested, he said.

Update at 5:01 p.m. ET: The head of the rebels' Transitional National Council said that pro-Gadhafi assailants had killed Younis and that the attackers have been arrested, the BBC reports.

Two of his aides also died, AP says.

Update at 4:36 p.m. ET: Abdel-Fattah Younis, who had headed the interior ministry under Moammar Gadhafi before defecting to the rebels in February, reportedly was arrested earlier today for dealing with and smuggling arms to Gadhafi loyalists, Al Jazeera says, noting the reports were unconfirmed.

He had served Gadhafi for nearly four decades.

"He spent 40 years as one of Gadhafi's right hand men as minister of defense and in charge of the special forces. So when he came over five months ago to the opposition cause it was quite a coup. But some people have had their doubts about… his loyalties...," Al Jazeera correspondent Tony Birtley said in Benghazi, the rebel capital.

Original post: The Libyan rebels' military commander has been killed, the leadership council in Benghazi says, the Associated Press is reporting.

The National Transitional Council announced the death of Gen. Abdel Fatah Younis, chief of staff of the rebel forces, just hours after he was arrested for allegedly continuing his ties to Moammar Gadhafi's regime. The circumstances of his death were not described.

He was held at a military garrison in Benghazi, capital of the rebel forces, after being recalled earlier today from Brega, a source told Al Jazeera.