An apparent NATO airstrike killed at least 10 rebel fighters on Wednesday in the northeast area of Misrata, officials said.
Opposition leaders said it was still unclear whether NATO bombs or rockets and shelling from Libyan leader Moammar Gadhafi's forces killed the men as they drove on a swampy road that leads directly to the port of the coastal city. But a doctor in Misrata told the Associated Press that the explosions did come from coalition aircraft.
Although an opposition spokesman told the Washington Post that 10 fighters died in the attack, the doctor told AP that 12 had been killed.
NATO had no immediate comment.
If the strike was by NATO warplanes, it would mark the third mistaken attack on rebel fighters in opposition territory since the airstrike campaign began several weeks ago.
On Tuesday, on the same road, NATO struck a convoy of 30 vehicles that belonged to Gadhafi's forces, rebel spokesman Mohamed Ali said. The group of four-wheel-drive vehicles was destroyed.
The port is the lifeline to the besieged city of Misrata, where more than 400 people have been killed in about two months of artillery fire, sniper fire and rocket attacks from Gadhafi's forces.
Recent attacks by Gadhafi loyalists have focused on the port in an attempt to disrupt the flow of humanitarian aid and weapons being shuttled to the rebels by sea. If the port becomes too dangerous, the rebels will have no access to supplies.
Rebel leaders therefore have begged for more NATO airstrikes, which they say will help save civilian lives. Even as some have denounced the civilian deaths from errant NATO strikes, the Western coalition has come under intense criticism for not doing more to stop Gadhafi's forces.
On Thursday, rebel leaders declined to fault NATO for the strike on the port road.
"If it was NATO, it means our boys are completely wrong to go there," Ali said, via Skype. "They were told not to go there by commanders, and we accept responsibility for this mistake. No one in Misrata is blaming NATO for what happened."
The Associated Press contributed to this report.