Dr Suleiman Refardi said Wednesday's raid happened in the village of Zawia el Argobe, 15km (9 miles) from Brega.
The strike hit a truck carrying ammunition, but the resulting explosion destroyed two nearby homes.
All the dead were between the ages of 12 and 20, Dr Refardi said. Nato says it is investigating the claim.
The news comes as opposition leader Mustafa Abdul Jalil said the rebels would agree to a ceasefire if Colonel Muammar Gaddafi's troops withdraw from cities.
"We agree on a ceasefire on the condition that our brothers in the western cities have freedom of expression and also that the forces that are besieging the cities withdraw," he told a news conference in the eastern rebel stronghold of Benghazi.
Dr Refardi told the BBC that Wednesday's coalition air strike hit a pro-Gaddafi ammunition truck and trailer in a street in Zawia el Argobe.
The resulting explosion caused a deadly hail of shrapnel, he said.
Four of the dead were female, including three children from the same family, aged between 12 and 16, the BBC's Ben Brown reports from Brega.
Three boys, aged between 14 and 20, were also killed.
Nato officials told the BBC they were making inquiries "down our operations chain to find out if indeed there is any information on the operation side that would support this claim".
Meanwhile, the BBC's Wyre Davies in Ajdabiya says rebel forces there are pressing on to the frontline around the oil town of Brega.
Plenty of enthusiastic, if disorganised, insurgents are driving through in pick-up trucks with heavy duty machine guns mounted on the back, he reports.