Rebel troops in Libya are calling on Nato to explain a "friendly fire" air strike on a column of rebel tanks that left at least four dead.
Gen Abdelfatah Yunis said he assumed the incident had been a mistake by Nato, but wanted a "rational and convincing explanation".
Nato has said it is investigating the claims.
It is the third such incident in recent days involving international forces deployed to protect Libyan civilians.
"We are not questioning the intentions of Nato, because they should be here to help us and the civilians," Gen Yunis told a news conference in Benghazi on Thursday.
"But we would like to receive some answers regarding what happened today."
He added: "We would assume it was Nato by mistake, friendly fire."
But if speculation in some quarters that the attack was carried out by Col Muammar Gadaffi's forces turned out to be true then it would be "a bigger mistake", he added.
"We're under a no-fly zone that should be protecting us from Gadaffi's aircraft," he said.
The rebels hit in the air strike had been moving a group of tanks, armoured vehicles and rocket launchers near the front line between the towns of Ajdabiya and Brega in more than 30 transporters.
One rebel commander told the BBC he saw at least four missiles land among rebel fighters.
Rebels said four rebels died, while local doctors told the BBC at least 13 fighters had been killed in the strike. Many more were injured.
There is considerable anger among rebel troops at what appears to have been a terrible mistake, the BBC's Wyre Davies, in Ajdabiya, said.
They are asking why rebel units were hit, he adds, when they could be seen clearly advancing in a westerly direction towards the front line.
"It is unbelievable," said one Benghazi resident. "Nato, with all the equipment they have - is this the second mistake? Is it really a mistake or something arranged secretly?"
Another said: "The allies and the UN Security Council must allow us to be armed. We don't want anything, just to be armed to defend ourselves against this dictator and fascist."
They had been calling for more Nato air strikes in recent days.
Nato said it was investigating the incident, noting that the area where the attack occurred was "unclear and fluid with mechanised weapons travelling in all directions".
"What remains clear is that Nato will continue to uphold the UN mandate and strike forces that can potentially cause harm to the civilian population of Libya," said the alliance in a statement.
Rebel forces in the area began retreating after heavy bombardment from government forces.
Our correspondent reported chaotic scenes on the outskirts of Ajdabiya, with rebels and civilians fleeing east along the coast road towards their stronghold of Benghazi.
The alliance took over air operations from a US, French and British coalition a week ago, to enforce a UN mandate to protect civilians in Libya.
Last Friday, at least 13 people were reportedly killed when a coalition plane fired on a rebel convoy between Brega and Ajdabiya.
Three medical students were among the dead.
The attack came after rebels reportedly fired an anti-aircraft gun.
In a separate incident, seven civilians died and 25 were hurt in a coalition air strike on a pro-Gaddafi convoy near Brega.
Further west, in Libya's third-biggest city, Misrata, a ship chartered by the UN World Food Programme delivered hundreds of tonnes of high energy biscuits, flour, and water purification tablets, as well as enough medicine to last 30,000 people for a month.
Misrata has been under attack by Libyan government forces for several weeks, and Libyan rebels have complained it would "cease to exist" within a week unless Nato took action to save it.