US and Egyptian special forces have reportedly been providing covert training to rebel fighters in the battle for Libya, Al Jazeera has been told.
An unnamed rebel source related how he had undergone training in military techniques at a "secret facility" in eastern Libya.
He told our correspondent Laurence Lee, reporting from the rebel-stronghold of Benghazi, that he was sent to fire Katyusha rockets but was given a simple, unguided version of the rocket instead.
"He told us that on Thursday night a new shipment of Katyusha rockets had been sent into eastern Libya from Egypt. He didn't say they were sourced from Egypt, but that was their route through," our correspondent said.
"He said these were state-of-the-art, heat-seeking rockets and that they needed to be trained on how to use them, which was one of the things the American and Egyptian special forces were there to do."
The intriguing development raises several questions, about Egypt's private involvement and what the arms embargo exactly means, said our correspondent.
"There is also the question of whether or not the outside world should arm the rebels, when in fact they [rebels] are already being armed covertly."
Our correspondent added that since the rebels appear to be receiving covert support in terms of weaponry and training, it is not surprising that they are not inclined to criticise NATO openly.
On Saturday the chief spokesman for the Libyan rebels said at least 13 people had been killed after coalition air strikes hit a convoy by mistake on Friday as fighters claimed victory in the battle for Brega.
"Thirteen dead, seven injured by friendly fire. It was a regrettable occurrence," Abdulhafiz Ghoga told a news conference, calling them "unintentional deaths".
|Rebels said Friday's NATO raid that killed at least 13 people was "collateral damage" [Reuters]
"The leadership is working on preventing a re-occurrence," he said, adding that Brega "is fully under the control of the rebels".
Brega has been the scene of intense exchanges over the past few days when pro-Gaddafi forces returned after being driven out by rebel forces.
But it has been unclear since Thursday who actually held the town, with anti-Gaddafi forces regrouping in Ajdabiya, about 80km the east.
Earlier, a civilian rebel official said the dead civilians were an ambulance driver and three medical students from Libya's second city of Benghazi.
They had been part of a rebel convoy of five or six vehicles, said Issa Khamis, liaison officer for the rebels' transitional government in the town of Ajdabiya, east of Brega.
Friday's air strike came as rebels shot tracer fire into the air to celebrate the entry of an advance column into Brega.
"It was a mistake" by the rebels, Khamis said. "The aircraft thought they were coming under attack and fired on the convoy."
A spokeswoman for NATO, which leads the international coalition enforcing the no-fly zone over Libya and protecting civilians from attack, said it was checking details of the incident.
"We are looking into these reports. We are always concerned by reports of civilian casualties. NATO's mission is to protect civilians and civilian areas from the threat of attack," said Oana Lungescu, adding that no formal investigation has been launched.
"We understand that collateral damage may also take place and we do accept it, because we look at the big picture which saving more lives"
Mustafa Gheriani, the opposition Transitional National Council
Speaking to Al Jazeera earlier, Mustafa Gheriani, a Transitional National Council spokesman, said the loss of lives on Friday was very much regretted.
"However, we understand that collateral damage may also take place and we do accept it, because we look at the big picture which saving more lives.
"So a few people being victims of circumstances or of being at the wrong time or the wrong place it is more or less very bad luck," Gheriani said.
The Libyan government, meanwhile, has produced a video said to show civilians, including women and children, in a Brega hospital. They are believed to have been wounded as they tried to escape the air strikes.
Doctors say more than 240 people have been killed and over 1,000 wounded in Misurata in the last month alone, as a counter-offensive by Gaddafi's troops raised the number of casualties.
On Saturday, the first three Swedish fighter jets landed in Italy as the Nordic country joins the NATO-led no-fly zone operation over Libya. Five more will leave for the mission on Sunday, Rickard Wissman, an air force spokesman, said.