Gen. Abdul Fattah Younis -- a longtime Gadhafi confidant who had been Libya's interior minister and a senior military officer before announcing Feb. 22 he defected to the rebels' side -- was killed along with two other senior opposition commanders by an armed gang, rebel government leader Mustapha Abdul Jalil said in a late-night news conference Thursday.
At least one gang member was captured, Jalil said without naming the member or saying whether he was allied with Gadhafi, rebels who did not trust Younis or some other tribal group or faction.
Jalil said "pro-Gadhafi" gunmen had infiltrated rebel-held areas.
The general -- who had an archrival for the army command, Khalifa Hifter, often creating confusion in the ranks -- usually traveled inside an armored car in a multivehicle convoy with 30 armed guards, posing problems for a potential assassination team, Britain's The Guardian reported.
The Times of London reported Younis was killed on the front line by his own troops after being arrested on suspicion of being on Gadhafi's payroll.
A Gadhafi spokesman said Younis, who Libyan state TV often reported had returned to his old job, was assassinated because the rebels believed he was working as a double agent.
Members of Younis' tribe -- the Obeidi, one of the largest and most powerful in eastern Libya -- blamed the rebel leadership for some role in the general's death, The New York Times reported.
Jalil confirmed Younis had been summoned for questioning by four judges working for the rebel council to "discuss military matters." Security officials earlier told al-Jazeera Younis was to be questioned about allegations his family still had ties to Gadhafi's government.
Jalil said Younis was later "released on his own recognizance," without saying whether Younis had been accused or exonerated of anything.
Younis' badly burned body and those of the two other officers, a colonel and a major, were recovered before Jalil made his announcement, a security officer said.
The killing and possible eruption of tribal animosities within Benghazi could damage the rebels' self-image as a movement bringing Libyans together under the banner of freedom and democracy, the Times said.
It could also shake international support for the opposition and rattle the divided rebel coalition, which this month gained U.S. recognition as Libya's sole governing authority, The Washington Post reported.
A senior Obama administration official in Washington said the White House was gathering details on Younis' death.
The administration had already begun reviewing a rebel request to open an embassy in Washington, State Department spokesman Mark Toner said.
There are fears among Western supporters of the rebels' National Transitional Council that its democratic goals could give way to a tribal civil war, the Times said.