The head of the Libyan rebel armed forces has been shot and killed just before arriving for questioning by rebel authorities, their political leader has said.
The carefully worded statement gave few details on who was behind the killing of Abdel Fattah Younes, who had defected from Colonel Gaddafi's regime where he had served as interior minister.
Hours earlier, the rebel National Transitional Council (NTC) had said that they had already detained the commander over suspicions his family might still have ties to the regime of Colonel Gaddafi.
The confusion has raised questions about whether he might have been assassinated by his own side.
But NTC chief Mustafa Abdel Jalil told reporters: "I ask you to refrain from paying attention to the rumours that Gaddafi's forces are trying to spread within our ranks."
Announcing Gen Younes' death, Mr Jalil said: "With all sadness, I inform you of the passing of Abdel Fatah Younes, the commander-in-chief of our rebel forces."
He said "the person who carried out the assassination was captured", but did not elaborate further.
Gen Younes had been called in from the front to answer questions over the military situation, Mr Jalil said, adding that there would be three days of mourning in his honour.
Gen Younes was part of the coup in 1969 that brought Colonel Gaddafi to power.
A spokesman for the Gaddafi regime claimed he was assassinated because the rebels believed he was working as a double agent.
News of the death came as rebel forces made some advances, seizing the town of Al-Ghazaya - used as a base by Gaddafis' troops to fire rockets - and Umm Al-Far, both near the Tunisian border.
Colonel Gaddafi had said he was ready to "sacrifice" in order to defeat the rebels.
"We are not afraid. We will defeat them," he said in an audio message, referring to the Nato alliance and the insurgents.
"We will pay the price with our lives, our women and our children. We are ready to sacrifice (ourselves) to defeat the enemy," he added in a message to loyalists in the town of Zaltan, also near the Tunisian border.