BENGHAZI, Libya (AP) - The Libyan rebels' military commander was killed by his comrades while in custody after he was arrested by the opposition's leadership on suspicion of treason, witnesses said Friday, in a sign of disarray that posed a major setback for the movement battling Moammar Gadhafi.
The slaying of Abdel-Fattah Younis raised fear and uncertainty in Benghazi, the de facto rebel capital. Thousands marched behind his coffin, wrapped in the rebels' tricolor flag, to the graveyard for his burial, chanting he was a martyr "beloved by God." Troops fired a military salute as the coffin arrived, and angry and grieving supporters fired wildly into the air with automatic weapons.
At the graveside, Younis' son, Ashraf, broke down, crying and screaming as they lowered the body into the ground and - in a startling and risky display in a city that was the first to shed Gadhafi's rule nearly six months ago - pleaded hysterically for the return of the Libyan leader to bring stability.
"We want Moammar to come back! We want the green flag back!" he shouted at the crowd, referring to Gadhafi's national banner.
Younis' slaying appeared to shake both the rebels' leadership body, the National Transitional Council, and its Western allies, who have heavily backed the rebels controlling most of eastern Libya.
Two weeks ago, 32 nations including the U.S. made a major commitment by formally recognizing the opposition as the country's legitimate government - a significant boost after many allies hesitated in part because the rebels, a mix of tribes and factions, were largely an unknown quantity.
Those Western worries will likely be deepened if Younis' slaying opens major splits among the fractious rebels. Divisions would also weaken the opposition's campaign to oust Gadhafi, which has largely stalled in a deadlock despite the four-month-old NATO bombing campaign against regime forces.
In Washington, State Department spokesman Mark Toner said the circumstances of Younis' death remained unclear, but he pressed the opposition to shore up any cracks in their front against Gadhafi.
"What's important is that they work both diligently and transparently to ensure the unity of the Libyan opposition," Toner said.
Younis' body was found Thursday, dumped outside Benghazi, along with the bodies of two colonels who were his top aides. They had been shot and their bodies burned.
Younis was Gadhafi's interior minister until he defected to the rebellion early in the uprising, which began in February, bringing his forces into the opposition ranks. His move raised hopes among rebels and Western allies that the uprising could succeed in forcing out the country's ruler of more than four decades. But some rebels remained deeply suspicious that he retained loyalties to Gadhafi.
The National Transitional Council says it is investigating the killing. It blamed unidentified "gunmen" and has made no confirmation Younis had been arrested.
It has said only that Younis was gunned down on route to Benghazi, where he had been summoned to discuss "a military matter."
"Everything is under control," the council's finance minister, Ali Tarhouni, told reportes Friday night. "This is just a rough stage we are going through and me and my brothers in the NTC are sure we will get over it."
But a rebel special forces officer under Younis' command told the Associated Press that Younis was taken before dawn Wednesday from his operations room at Zoueitina, just east of the main front with Gadhafi's forces.
Fighters from a rebel faction known as the February 17 Martyr's Brigade came to the operations room and demanded Younis come with them for interrogation, said the officer, Mohammed Agoury, who said he was present at the time.
Agoury said he tried to accompany his commander, "but Younis trusted them and went alone."
"Instead, they betrayed us and killed him," he said.
The February 17 Martyrs Brigade is a group made up of hundreds of civilians who took up arms to join the rebellion. Their fighters participate in the front-line battles with Gadhafi's forces but also act as a semi-official internal security force for the opposition. Some of its leadership comes from the Libyan Islamic Fighting Group, an Islamic militant group that waged a campaign of violence against Gadhafi's regime in the 1990s.
An officer with the rebels' internal security forces - the official security force of the National Council - told AP that the council ordered Younis' arrest after a letter arose earlier this week connecting the commander to Gadhafi. But he suggested the killing had not been authorized by the council and was instead an act of vengeance by rebels.
He said Younis was brought back to the Benghazi area Wednesday and held at a military compound until Thursday, when he was summoned to the Defense Ministry for questioning.
As they left the compound, two men from the security team escorting the detainees opened fire on Younis from their car with automatic weapons, said the officer, who was at the compound and saw the shooting. He said the two men were members of the February 17 Martyrs Brigade and shouted that Younis was a traitor who killed their father in Derna, an eastern town that was once a stronghold of the LIFG.
"The men's leader was shouting, "Don't do it!' but they shot Younis and his two aides, and took their bodies in their car and drove away," the officer said. He spoke on condition of anonymity because he was not authorized to discuss the events.
Officials from the National Transitional Council could not immediately be reached for comment on the witnesses' version of the events.
Agoury said the Martyrs Brigade had an agenda against Younis, because while with the regime he was involved in the bloody crackdown that crushed the LIFG.
"They don't trust anyone who was with Gadhafi's regime. They wanted revenge," Agoury said.
A member of the Martyr's Brigade said his group had evidence Younis was a "traitor." He told the AP "the evidence will come out in a few days." The brigade member spoke on condition of anonymity because he feared reprisals.
From Tripoli, Gadhafi's deputy foreign minister, Khaled Kaim, said the regime's forces had no role in Younis' death. He called for a forensic investigation of Younis' remains, saying even though he was a "traitor" to the government "he was still a Libyan citizen."
The city of Benghazi woke up to fierce shooting Friday, as the news of Younis' death spread confusion and suspicion. Among those firing were members of Younis' powerful Obaidi tribe.
Britain, one of the major participants in NATO's anti-Gadhafi bombing campaign, condemned the killing, but was cautious in its response.
"Exactly what happened remains unclear," said Foreign Office Minister Alistair Burt. He said he had spoken to the rebels' political leader, who had stressed "the killing will be thoroughly investigated."
"We agreed that it is important that those responsible are held to account through proper judicial processes," Burt said.
NATO spokeswoman Carmen Romero said the alliance had no comment on the incident.
France, another key member of the anti-Gadhafi alliance, said the French had not received any new operational orders from NATO since the death was announced. He suggested that a single individual's absence would not signal a major shift, saying the operation was based on a U.N. mandate "and it does not let individual people feature in the game."
France's Le Monde newspaper took a harsher view, warning that the rebels' version of events "is hardly reassuring" and gives reason "to doubt the capacity of the council to exercise power."
"This risks reinforcing Tripoli's hand," Le Monde wrote.