The head of the Libyan rebels' armed forces and two of his aides have been killed by gunmen, the head of the rebel leadership said.
The death of Abdel-Fattah Younis was announced at a press conference in the de facto rebel capital, Benghazi, by the head of the rebels' National Transitional Council, Mustafa Abdul-Jalil.
He told reporters that rebel security had arrested the head of the group behind the killing.
Rebel security had arrested Mr Younis and two of his aides early on Thursday from their operations room near the rebels' eastern front. Security officials said at the time that Mr Younis was to be questioned about suspicions that his family still had ties to Muammar Gaddafi's regime.
Mr Younis was Gaddafi's interior minister before defecting to the rebels early in the uprising, which began in February.
Mr Abdel-Jalil said Mr Younis had been summoned for questioning regarding "a military matter". He said Mr Younis and his two aides were shot before they arrived for questioning.
Mr Abdel-Jalil called Mr Younis "one of the heroes of the 17th of February revolution", a name marking the date of early protests against the Gaddafi regime.
While he criticised Gaddafi for seeking to break the unity of rebel forces, he did not say directly that Mr Younis's killers were associated with the regime.
Instead, he issued a stiff warning about "armed groups" in rebel-held cities, saying they needed to join the fight against Gaddafi or risk being arrested by security forces.