AJDABIYA, Libya -- An apparent NATO airstrike slammed into a rebel combat convoy Thursday, killing at least five fighters and sharply boosting anger among anti-government forces after the second bungled mission in a week blamed on the military alliance.
The attack -- outside the strategic oil port of Brega -- brought fresh questions about coordination between NATO and the patchwork of rebel militias in a conflict described by a senior U.S. commander as a stalemate that could eventually require the Pentagon to reassert more power, and possibly even send in ground forces.
Tensions between the rebels and NATO were flaring even before the latest accident, with the fighters criticizing the alliance for doing too little to help them.
In a sign of the hair-trigger tensions along the front, thousands of civilians and fighters raced out of the rebel-held city of Ajdabiya in eastern Libya after reports that Moammar Gadhafi's forces gained ground in the chaos after the bombing. Some militiamen shouted insults against NATO as they retreated.
"We don't want NATO anymore!" cried fighter Basit bin Nasser. Another yelled: "Down, down with NATO."
In Brussels, NATO did not directly acknowledge responsibility for a blundered airstrike on the rebels but noted that the area where the attack occurred was "unclear and fluid with mechanized weapons traveling in all directions."
"What remains clear is that NATO will continue to uphold the U.N. mandate and strike forces that can potentially cause harm to the civilian population of Libya," the alliance said in a statement.
But NATO faces the same challenges to avoid friendly fire deaths as commanders in other wide-ranging air missions such as Iraq and Afghanistan.
The rebels lack the high-grade communications and surveillance systems to coordinate with NATO planners and pilots.
And from above, both sides may appear very similar. Rebels used seized tanks and vehicles from the Libyan military. The pro-Gadhafi forces, meanwhile, are increasingly mixing into civilian areas and adopting the guerrilla-style appearance of their foes.
A NATO official said there is growing frustration with the rebels' perception that NATO is acting as their proxy air force. The U.N. mandate calls only for international air power to enforce a no-fly zone and prevent attacks on civilians -- although Gadhafi's ground forces remain a primary target.
"We're trying to get messages back to them about what we're doing and what we're trying to achieve," said the official, who spoke on condition of anonymity under standing NATO regulations.
Last week, NATO took control over the international airstrikes that began March 19 as a U.S.-led mission. The airstrikes thwarted Gadhafi's efforts to crush the rebellion he has ruled for more than four decades, but the rebels remain outnumbered and outgunned and have had difficulty in making headway into government-held territory.
The U.S. general who led the Libyan mission before NATO's takeover said Washington still provides some strike aircraft to NATO including powerful side-firing AC-130 gunship.
Army Gen. Carter Ham even predicted that the Pentagon may be forced one day to consider ground forces in Libya if the battle lines remain indefinitely stalled. But he noted any such decision would open America to serious political fallout for intervention in another Muslim nation.
"I suspect there might be some consideration of (ground forces). My personal view at this point would be that that's probably not the ideal circumstance, again for the regional reaction that having American boots on the ground would entail," Ham told a Senate Armed Services Committee hearing.
President Barack Obama has said repeatedly there will be no U.S. troops on the ground in Libya, although there are reports of small CIA teams in the country.
The rebels have controlled eastern Libya since early on in the uprising and much of the fighting takes place along a highway on the country's northern Mediterranean coast, where the opposition has tried to advance west toward the capital Tripoli.
The airstrikes Thursday came as rebels forces pushed toward the outskirts of Brega, an eastern oil port that has traded handed several times since the revolt began in February.
A rebel commander, Ayman Abdul-Karim, said he saw airstrikes hit tanks and a rebel convoy, which included a passenger bus carrying fighters toward Brega. He said the tops of rebel vehicles were marked with yellow under advice by NATO to identify the opposition forces
An official at nearby Ajdabiya Hospital, Dr. Mohamed Idris, said at least five people were killed and 22 injured, including some with serious burns. Idris said other casualties were left in the field in the chaos to flee the area.
The small medical facility was overwhelmed. One rebel sat in a hallway, wrapping gauze around his injured leg.
In the rebels de facto capital Benghazi, opposition spokeswoman Iman Bughaigis said the death toll could be as high as 13.
"People are very upset and the street is really boiling," she said.
Last Friday, a NATO airstrike killed 13 rebel fighters in eastern Libya. An opposition spokesman described it as an "unfortunate accident" in the shifting battles and pledged support for the international air campaign to weaken Gadhafi's military power.
But rebel discontent with NATO appears to be growing. Opposition commanders have complained in recent days that the airstrikes were coming too slowly and lacking the precision to give the rebels a clear edge.
Rebels also have turned to the oil fields under their control as a source of money for weapons and supplies. The Liberian-flagged tanker 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 have crippled production. Libya claimed British jets waged the bombings. NATO, however, dismissed the accusations and blamed Gadhafi's forces.
"We are aware that pro-Gadhafi forces have attacked this area in recent days," said Canadian Lt. Gen. Charles Bouchard, who commands the allied operation. "To try and blame it on NATO shows how desperate this regime is."
In the capital, Tripoli, former U.S. congressman Curt Weldon met with a senior Libyan official and said it was time for Gadhafi to step 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 the former Pennsylvania lawmaker, who has visited Libya several times as Washington rebuilt ties with Gadhafi.
Weldon said he came to Libya on the invitation of Gadhafi, but the trip has no ties with the U.S. government.
In Seattle, Microsoft Corp. said it was working to free its manager in charge Libyan operations who has been held since March 19. Microsoft said it had no information about the reasons for Khalid Elhasumi's detention.
Meanwhile, a former Gadhafi loyalist, Libya's ex-energy minister Omar Fathi bin Shatwan, has held talks with British and other European diplomats to discuss the state of Gadhafi's regime. He told The Associated Press on Wednesday that he had fled to Malta on a fishing vessel.
In London, officials said an international group overseeing political initiatives on Libya is scheduled to hold its first meeting next Wednesday in Qatar, one of the few Arab nations contributing aircraft to the NATO mission. The so-called "contact group" includes European nations, the United States, allies from the Middle East and international organizations.
Associated Press writer Hadeel al-Shalchi in Tripoli, Libya, and Slobodan Lekic in Brussels contributed to this report.