Libyan rebels in Benghazi said they were investigating the assassination of rebel army chief General Abdel Fatah Yunis while the regime of Moamer Kadhafi pinned the blame on Al-Qaeda.
"The NTC has appointed an investigative committee and we will publish all the facts of this investigation," said Ali Tarhuni, who handles economic affairs for the rebel National Transitional Council.
Yunis was the faithful right-hand man of Kadhafi, participating in the 1969 coup that brought him to power, before defecting to rebels who have been fighting to oust the strongman since February.
Tarhuni said the general's bullet-riddled and partly burned body was found early Friday on the outskirts of Benghazi but that the NTC had received news of the crime late Thursday when the head of a militia behind the crime confessed.
"The head of the militia is imprisoned now," he said, adding that some of the perpetrators, who he said belonged to Jirah Ibn al-Obeidi brigade, were yet to be incarcerated, while the motives for the crime remained unclear.
"We don't know who they work for," he said.
Tripoli meanwhile developed its theory.
"By this act, Al-Qaeda wanted to mark out its presence and its influence in this region" of eastern Libya controlled by the rebels fighting to overthrow Kadhafi, regime spokesman Moussa Ibrahim told reporters.
"The other members of the National Transitional Council knew about it but could not react because they are terrified of Al-Qaeda," he added.
A dozen explosions meanwhile shook the Libyan capital Tripoli late Friday and early Saturday -- the latest of many blasts in a city which has been targeted almost daily by NATO air raids.
An announcer on Al-Jamahiriya television said the Libyan TV headquarters had been hit by a raid. He gave no further details.
Yunis's death on Thursday, and that of two officers with him, left rebels facing a leadership crisis and a whirlpool of rumours on the same day they made fresh gains in the western Nafusa mountain range.
The United States urged the rebels to stand united and stay focused on ousting Kadhafi and blamed him for creating the conditions that led to the murder.
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State Department spokesman Mark Toner said rebels should "work both diligently and transparently to ensure the unity of the Libyan opposition."
"Such tragedies speak to the situation that's been created by Kadhafi and his regime. It underscores why he needs to leave power and do so immediately."
Portugal meanwhile became the latest country to recognise the NTC.
In London, Britain's minister for the Middle East and North Africa, Alistair Burt, condemned the assassination and extended his condolences to NTC Chairman Mustafa Abdel Jalil.
"We agreed that it is important that those responsible are held to account through proper judicial processes," he said.
The mysterious assassination of Yunis, Libya's former interior minister, sparked speculation that he was killed for treason by one of the two warring camps.
A senior opposition figure in Benghazi accused Kadhafi of playing a role in the killing in an attempt to get rebels to back off from strategic oil town Brega.
"All these are signs Kadhafi was behind it," the official told AFP.
Yunis was killed as he returned from the front line, which lies near Brega.
"Whoever took part in this crime will be brought to justice no matter who they are," Tarhuni said.
The scenario that the unity of rebels in the east -- where there are more than 30 brigades -- may be cracking could be awkward for the many Western powers who have recognised the NTC as the sole legitimate authority in Libya.
"The NTC hasn't been able to make any clear, credible statements about Yunis because they don't really know what's going on," said Lynette Nusbacher, senior lecturer in war studies at Britain's Royal Military Academy Sandhurst.
Some rebels viewed Yunis with mistrust -- a potential Tripoli informer rather than a true regime defector.
"Nobody wanted him alive except maybe his mother," Nusbacher said.
Libyan rebels meanwhile said a loan from Turkey had arrived and that they hoped to reach out with food and monetary aid to fighters and their families in the west of the country during Ramadan.