Rebel fighters take cover in a cave at the frontline, at the northwestern city of Nalut, some 200 km (125 miles) southwest of Tripoli, June 18, 2011. [Photo/Agencies]

TRIPOLI, Libya - NATO said Saturday it mistakenly struck a column of Libyan rebel vehicles in an airstrike near an eastern oil town two days earlier and expressed regret for any casualties that might have resulted.

The alliance has accidentally hit rebel forces before in its air campaign to protect civilians in the civil war between Moammar Gadhafi's military and the fighters trying to end his more than four decades in power. The rebels have also complained that NATO's strikes have not helped them gain decisive momentum against the Libyan leader's better trained and equipped military, which still has firm control over most of western Libya. The rebels control much of the east.

The alliance statement gave no figures on casualties from Thursday's airstrike, but said it regretted "any possible loss of life or injuries caused by this unfortunate incident."

NATO said its forces spotted a column of military vehicles near the frequent flashpoint town of Brega where forces loyal to Gadhafi had recently been operating and hit them because they believed they posed a threat to civilians.

"NATO can now confirm that the vehicles hit were part of an opposition patrol," the statement said.

There was no immediate comment from the rebel leadership.

International military forces have had some trouble in hitting government troops because of their proximity to civilians. Gadhafi's troops have also used civilian vehicles, making them difficult to distinguish from rebel forces.

Thursday's airstrike was similar to one on April 7 in which NATO hit a convoy of rebel tanks, killing at least five fighters, as the rebels were closing in on Brega. NATO officials said at the time they did not know the rebels had any tanks, a statement that raised eyebrows as footage of the rebels with tanks had been on YouTube for weeks.

A week earlier, NATO also mistakenly targeted rebels as they tried to retake Brega. The rebels said 13 of their fighters were killed in that attack.

Earlier Saturday, NATO accused Gadhafi's forces of using mosques and children's parks as shields for his military operations and said the Libyan leader is "brutally attacking" his people.

At least two explosions shook the capital, Tripoli, Saturday as NATO jets soared above the city, hours after Gadhafi lashed out against airstrikes in a speech Friday night, insisting "NATO will be defeated." It was not immediately clear what had been hit or if any casualties were reported.