AJDABIYA, Libya - (AP) - Rebel fighters claimed NATO airstrikes blasted their forces Thursday in another apparent mistake that sharply escalated anger about the military alliance's efforts to cripple Libyan forces. At least five rebels were killed and more than 20 injured, a doctor said.

The attack - near the front lines outside the eastern oil portof Brega - would be the second accidental NATO strike against rebelforces in less than a week. It brought cries of outrage fromfighters struggling against Moammar Gadhafi's larger and moreexperienced military.

"Down, down with NATO," one fighter shouted as dozens of rebelvehicles raced eastward from the front, toward the rebel-held cityof Ajdabiya.

Later, hundreds of cars poured out of Ajdabiya toward the defacto rebel capital, Benghazi, amid fears that pro-Gadhafi forcescould use the disarray among rebel units to advance along theMediterranean coastal road that serves as the lifeline for bothsides.

In Brussels, a NATO official said the alliance will look intothe latest rebel claims but he had no immediate information. Theofficial spoke on condition of anonymity under standingregulations. In a separate statement, NATO dismissed Libyan claimsthat British warplanes struck the country's largest oil field,saying the attacks were carried out by government forces.NATO last week took control over the international airstrikesthat began March 19 as a U.S.-led mission. The airstrikes thwartedGadhafi's efforts to crush the rebellion in the North Africannation he has ruled for more than four decades, but the rebelsremain outnumbered and outgunned and have had difficulty pushinginto government-held territory even with air support.

In Washington, Army Gen. Carter Ham - who led the initial phasesof the Libyan mission before transferring command to NATO -described the conflict as a stalemate and said Gadhafi's forces aremaking airstrikes more difficult by mixing into civilian areas.

A rebel commander, Ayman Abdul-Karim, said he saw airstrikes hittanks and a rebel convoy, which included a passenger bus carryingfighters toward Brega. He and other rebels described dozens killedor wounded, but a precise casualty toll was not immediately known.

An official at Ajdabiya Hospital, Dr. Mohammad Idris, said atleast five people were killed and 22 injured, including some withserious burns. Idris said other casualties were left in the fieldin the chaos to flee the area.

In Benghazi, opposition spokeswoman Iman Bughaigis said thedeath toll could be as high as 13.

The small medical facility was overwhelmed. One rebel sat in ahallway, wrapping gauze around his injured leg.

Last Friday, a NATO airstrike killed 13 rebel fighters ineastern Libya. An opposition spokesman described it as an"unfortunate accident" in the shifting battles and pledgedsupport for the international air campaign to weaken Gadhafi'smilitary power.

On Thursday, NATO said the situation where the strike occurredwas "unclear and fluid with mechanized weapons traveling in alldirections."

"What remains clear is that NATO will continue to uphold theU.N. mandate and strike forces that can potentially cause harm tothe civilian population of Libya," the alliance said.

But rebel discontent with NATO appears to be growing. Oppositioncommanders have complained in recent days that the airstrikes werecoming too slowly and lacking the precision to give the rebels aclear edge. NATO officials say that the pro-Gadhafi troops haveblended into civilian areas in efforts to frustrate the alliancesbombing runs.

The rebel commander Adbul-Karim said the tops of rebel vehicleswere marked with yellow under advice by NATO to identify theopposition forces. But rebels use tanks and other vehiclescommandeered from the Libyan army - potentially making theirconvoys appear similar to pro-government units from the air.

The attack occurred about 18 miles (30 kilometers) from Brega,where rebel forces have struggled to break through governmentlines, he said.

Rebels also have turned to the oil fields under their control asa source of money for weapons and supplies. The Liberian-flaggedtanker Equator, which can transport up to 1 million barrels of oil,left the eastern port of Tobruk en route to Singapore on Wednesday,oil and shipping officials said.

But sustained attacks on the main rebel-held oil fields havecrippled production. Libya claimed British jets waged the bombings.NATO, however, dismissed the accusations and blamed Gadhafi'sforces."We are aware that pro-Gadhafi forces have attacked this areain recent days," said Canadian Lt. Gen. Charles Bouchard, whocommands the allied operation. "To try and blame it on NATO showshow desperate this regime is."

In the capital, Tripoli, former U.S. congressman Curt Weldon metwith a senior Libyan official and said it was time for Gadhafi tostep down and hand power to an interim government.

The meeting between Weldon and Libya's prime minister,Al-Baghdadi al-Mahmoudi, was part of a private mission by theformer Pennsylvania lawmaker, who has visited Libya several timesas Washington rebuilt ties with Gadhafi.

Weldon said he came to Libya on the invitation of Gadhafi, butthe trip has no ties with the U.S. government.Meanwhile, a former Gadhafi loyalist, Libya's ex-energy ministerOmar Fathi bin Shatwan, has held talks with British and otherEuropean diplomats to discuss the state of Gadhafi's regime. Hetold The Associated Press on Wednesday that he had fled to Malta ona fishing vessel.

In London, officials said an international group overseeingpolitical initiatives on Libya is scheduled to hold its firstmeeting next Wednesday in Qatar, one of the few Arab nationscontributing aircraft to the NATO mission. The so-called "contactgroup" includes European nations, the United States, allies fromthe Middle East and international organizations.

Former U.S. rep in Libya for talks with GadhafiGovernment bombardment pushes back Libyan rebelsU.S. soon ending air combat role in Libya