Unclear was whether the airstrike was by Libyan military loyal to strongman Moammar Gadhafi or by planes of the NATO alliance whose mission is to protect citizens from Gadhafi, CNN reported.
A NATO representative in Brussels said the coalition is looking into the report. If the alliance did conduct the deadly airstrike, it would be the second strike within a week in which rebels were killed in the Brega area, a spokesman for the rebels said. NATO also is investigating the earlier attack in which at least 13 rebel fighters died.
The latest violence comes as pro-Gadhafi forces battle opposition fighters demanding democracy and an end to Gadhafi's four decades of rule.
In Tripoli, four explosions were heard and two aircraft could be seen overhead Thursday, CNN reported.
A Libyan government official said British warplanes hit a major Libyan oilfield on Wednesday, killing three civilian guards, injuring scores of workers and damaging a pipeline, The Guardian reported.
"British warplanes have attacked, have carried out an air strike against the Sarir oilfield which killed three oilfield guards, and other employees at the field were also injured," Khaled Kalim, the regime's deputy foreign minister, told reporters in Tripoli. "There is no doubt that this aggression ... is against international law and is not covered by the U.N. resolution."
Former U.S. Rep. Curt Weldon, R-Pa., was in Libya to meet with Gadhafi and tell him he needs to leave power, CNN reported. Weldon arrived in Tripoli Wednesday at Gadhafi's invitation, but aides said Thursday it was unclear when Weldon and Gadhafi would meet.
It was revealed that Gadhafi recently sent a letter to President Obama, urging the president to end the "unjust war against a small people of a developing country" and called those in the opposition terrorists and members of al-Qaida, a White House official said.