The rebels were on their way to Brega when they fired into the air with an anti-aircraft gun, the BBC's Nick Springate reported from the scene of the attack.
Rebel fighter stands beside a car burnt in what rebels say was a coalition air strike on a group of vehicles on the road between Brega and Ajdabiya - 02 April 2011 The rebel convoy was on its way to the front line near Brega when the attack took place
The road to the front line is riddled with holes caused by what looks like a Nato A10 aircraft, our correspondent says.
On either side of the road are the remains of four pick-up trucks and one ambulance as well as the graves of those killed in the attack, he adds.
The attack is thought to have happened between 2300 and midnight local time. There is very little clarity surrounding the incident, but an anti-aircraft gun may have been fired in celebration, our correspondent says.
A coalition plane then opened fire on the convoy, destroying the five vehicles, the rebels said.