Nato is investigating reports from Libyan rebels that a coalition warplane struck one of their positions that was firing into the air near the front line of the battle with Muammar Gaddafi's forces.
Rebels said a group of opposition fighters was hit by an airstrike about 12 miles (20 kilometres) east of the town of Brega last night.
Mohammad Bedrise, a doctor in a nearby hospital, said three burned bodies had been brought in by men who said they had been hit after firing a heavy machine gun in the air in celebration.
Idris Kadiki, a 38-year-old mechanical engineer, said he had seen an ambulance and three cars burning after an airstrike.
Nato spokeswoman Oana Lungescu said the coalition was looking into the reports.
The loosely organised rebel force have been acting in a more disciplined fashion in recent days.
Yesterday only former military officers and the lightly trained volunteers serving under them were allowed on the front lines. Some were recent arrivals, hoping to rally against forces loyal to the Libyan leader, which have pushed rebels back about 100 miles (160 kilometres) this week.
The better-organised fighters, unlike some of their predecessors, can tell the difference between incoming and outgoing fire. They know how to avoid sticking to the roads, a weakness in the untrained forces that Gaddafi's troops have exploited.
It is a sign that military people who have split from the regime to join the rebellion are finally taking a greater role in the fight after weeks trying to organise.
Fighters cheered yesterday as one of their top commanders - former Interior Minister Abdel-Fattah Younis - drove by in a convoy toward the front.
But it is too early to say if the improvements will tip the fight in the rebels' favour. They have been struggling to exploit the opportunity opened by international airstrikes that have been hammering Gaddafi's forces since March 19.
In a sign the strikes may be eroding Gaddafi's resilience, his government is trying to hold talks with the US, Britain and France in hopes of ending the air campaign, said Abdul-Ati al-Obeidi, a former Libyan prime minister who has served as a Gaddafi envoy during the crisis.
"We are trying to find a mutual solution," he told Channel 4 News.
British officials met with Mohammed Ismail, a Libyan government aide who happened to be in London visiting relatives, and told him Gaddafi must quit, two people familiar with the issue said.
The opposition said yesterday in Benghazi, its de facto capital, it will agree to a cease-fire if Gaddafi pulls his military forces out of cities and allows peaceful protests against his regime.
The rebel condition is that "the Gaddafi brigades and forces withdraw from inside and outside Libyan cities to give freedom to the Libyan people to choose," said Mustafa Abdul-Jalil, head of the opposition's interim governing council. "The world will see that they will choose freedom."
Gaddafi's forces continue to attack rebels in the east, which is largely controlled by the opposition, and have besieged the only major rebel-held city in the west, Misrata.
Misrata has been shelled by tanks and artillery for days, said a doctor in a city hospital.
Many people have been killed, including eight since Thursday, he said. He said Gaddafi brigades control the port and a main street, but rebels control the heart of the city.