Eastern Libyan authorities have resumed an investigation into the unexplained killing of a top rebel commander in the 2011 uprising that toppled Muammar Gaddafi, a case that could reopen old wounds.

The unsolved killing of Abdel Fattah Younes by suspected fellow fighters in 2011 caused deep rifts inside the rebel camp of the kind that have marked the turmoil and violence gripping Libya ever since.

The investigation risks stirring new tensions between eastern Libya, controlled by the forces of General Khalifa Haftar, and a U.N.-backed administration in the capital Tripoli.

Haftar ordered the eastern military prosecutor to "immediately and urgently reopen the investigation" of the killing of Younes and two others slain in 2011, according to a decree posted late on Monday.

A previous investigation launched in 2011 had named as prime suspect Ali Essawi, who was deputy prime minister during the uprising at a rebel transitional authority which took over power from Gaddafi.

A court later dropped the case against Essawi and other suspects. But Essawi resurfaced into the spotlight when Tripoli-based Prime Minister Fayez appointed him as economy minister this month.

His appointment had sparked angry reactions from Younes's Obeidat tribe and a second eastern-based tribe, who warned in comments published on local media that the move was a provocation.

Both tribes are among the most powerful in the east and allied to Haftar, who has conquered most of eastern Libya.

The United Nations has been trying to mediate between east and west in a bid to overcome divisions and prepare the North African country for elections.

France had been pushing for the vote in December but recent fighting between rival groups in Tripoli and a lack of a constitutional basis has dimmed the prospect.

Younes was for years part of Gaddafi's inner circle.

He defected at the start of the uprising in February 2011 and became the military chief of the rebellion, a move opposed by other rebels who had suffered under the old regime.

His death caused deep rifts within the rebellion, exposing tensions between Islamists - whom Gaddafi fiercely suppressed during his 42-year dictatorship - and secularists and former army figures, with various factions accusing each other of responsibility.

The circumstances of his killing remain murky, but it is known that he was slain in July 2011 after rebel leaders summoned him back from the front line to Benghazi, the eastern city and cradle of the uprising.