Rebel forces in eastern Libya have received covert military training from US and Egyptian special forces, according to a report in Al Jazeera.

Quoting an unnamed source affiliated with rebels seeking to topple Moammar Gaddafi, US and Egyptian military specialists are providing training at a secret facility in eastern Libya.

An Al Jazeera reporter based in the rebel stronghold in Benghazi said [The rebel official] 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. 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.

Al Jazeera indicated that this surprising development raises some thorny issues, given that Egypt had not yet had any involvement in its neighbor’s turmoil, and the fact that the United Nation’s no-fly zone resolution prohibits supplying of arms to anyone in Libya.

Al Jazeera commented: 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.

Meanwhile, at least thirteen rebels were accidentally killed and more injured by coalition air strikes near Brega on Friday.

NATO has expressed its concern over the “unintentional” deaths.

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 NATO spokesperson Oana Lungescu. 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