BENGHAZI, Libya — Libya’s rebel military struggled Saturday to explain an apparent rift within its highest ranks while acknowledging its soldiers’ role in a mistaken NATO bombing of rebel columns the night before.

A NATO airstrike intended to thwart Moammar Gadhafi’s forces killed 13 rebel fighters in eastern Libya instead, the opposition said Saturday, but they described it as an “unfortunate accident” and stressed it did not diminish their support for the international air campaign.

The strike illustrated the hazards of conducting an aerial bombing campaign against a fluid and fast-moving front line. Several cars and an ambulance were also incinerated, and opposition leaders said rebels may have been responsible for the bombing because they had fired their guns into the air in celebration.

The rebels’ response to the attack — blaming it on a mistake within their ranks — highlighted their heavy dependence on the international air campaign as they face the superior military power of the longtime Libyan leader.

The misfire also showed the challenges the coalition faces in identifying targets without coordination with forces on the ground.

The incident came as the rebels and forces loyal to Gadhafi increasingly appear locked in stalemate, with rebels controlling most of the eastern part of the country but unable to oust Gadhafi from power. The government has rejected a rebel-proposed truce that would essentially leave the country divided in half.

The rebel force has been criticized for its inexperience — many of the soldiers had never picked up a weapon before the uprising against Gadhafi began — and it narrowly missed being routed in March when coalition planes halted Gadhafi’s forces as they reached Benghazi, the rebel capital.

The opposition has said soldiers have started to receive better training and clearer leadership in the past week. But a day after the strike, the interim government sought to distance itself from a popular army commander it had earlier embraced.

Khalifa Haftar, a former army colonel who recently returned to Libya after living for many years in Falls Church, Va., was initially hailed by the Transitional National Council as a leader who could help discipline the new army and train its largely volunteer ranks.

But Saturday, Ghoga said Haftar had no leadership role in the army.

“We defined the military leadership before the arrival of Haftar from the United States,” he said, referring to the appointment of Abdul Fattah Younis as commander of the armed forces and Omar al-Hariri as the council’s senior defense official. “We told Mr. Haftar that if he wants, he can work within the structure that we have laid out.”

However, a source within the military who is close to Haftar said Haftar is still commanding the army, and that Ghoga’s announcement had upset the public.

Sorting rebels from Gadhafi’s forces has become more difficult recently, as some loyalists have given up tanks and other armored vehicles for the kind of equipment the rebels rely on: pickup truck and other vehicles equipped with makeshift armaments.

NATO, which on Thursday took over what had been a U.S.-led military campaign to stop Gadhafi from attacking his own people, also is investigating whether other airstrikes have killed civilians in western Libya, as the Libyan government claims. The United States, meanwhile, was ending its role in combat missions Saturday, leaving that work for other nations.

On Saturday, U.S. combat aircraft flew 24 strike missions in Libya, the Pentagon said. But starting today, no U.S. combat aircraft are to fly strike missions in Libya. NATO’s on-scene commander can request American strikes in the days ahead, in which case they may have to be approved in Washington.

In Syria, meanwhile, security agents tightened security and made sweeping arrests Saturday as President Bashar Assad tried to cut off two weeks of deadly pro-democracy demonstrations that are threatening his family’s ruling dynasty. U.N. Secretary-General Ban Ki-moon expressed deep concern about the violence and called on Syria’s government to address the “legitimate aspirations of the Syrian people.”