A Libyan rebel fighter, holding a rocket launcher, shouts religious slogans Friday after gunshots were heard as fellow comrades offer prayers in the background in Ajdabia, Libya. Rebel fighters sent scouts Friday toward the contested oil port of Brega to seek clues on whether pro-government forces took advantage of a mistaken NATO airstrike that pounded opposition tanks and sent survivors into retreat.

Brussels ? NATO holds its fire as Moammar Gadhafi’s forces advance 100 miles into rebel territory. It then blasts a rebel tank, saying it didn’t know the rebels had any — even though footage of rebels with tanks had been on YouTube for weeks.

NATO’s leadership of the Libya campaign is coming under increasing criticism for mistakes and ineffectiveness. Nine difficult days of leading the air war have brought into sharp relief the confusion, ambiguity and constraints of the alliance’s mission.

“This is something new. We haven’t had a significant military operation in which the Americans have taken a back seat for quite some time,” Malcolm Chalmers, a professor of defense at London’s Kings College, said Friday. “It really is unclear whether the Europeans can rise to that challenge.”

The NATO bombing of a rebel convoy on Thursday, in which five people died and at least one rebel tank was destroyed, appears to have crystalized the perception — to outsiders, at least — that the alliance is running a bumbling campaign.

Misfires are not uncommon during air operations. And in NATO’s defense, poor visibility from thick clouds and sandstorms whipped up by brisk sea breezes has limited the targets — particularly during the lightning counterattack by Gadhafi forces early last week. Government forces pushed about 100 miles eastward from Gadhafi’s hometown of Sirte past rebel forward positions at Bin Jawwad, pushing the rebels back to Ras Lanuf and later to Brega, where the front is now.

Further complicating the military campaign has been a lack of human spotters on the ground — CIA agents in Libya are said to be gathering intelligence on the organizational structure of the rebel movement rather than coordinating airstrikes — and no established network for NATO and the ragtag group of rebels to communicate.

But as the rebels angrily accused the alliance of mistakes and neglect, NATO’s frustrated leaders refused to apologize Friday for the bombing of the tanks. And NATO commanders, in turn, are frustrated that the rebels see NATO as their proxy air force, rather than a force to protect civilians in Libya.

There is significant ambiguity about the scope and objective of the mission. The U.N. resolution under which the alliance operates requires it to protect civilians from Gadhafi’s forces while remaining impartial.

“There’s a very difficult trade-off for NATO here,” Chalmers said. “If they wait until they’re absolutely certain that they’ve got the targets right and that there are no civilians, Gadhafi’s forces will have vanished in the confusion by then.”

Adding to NATO’s woes, the U.S., which handed off its leadership role March 31, halted its combat role this week. That move is depriving NATO of certain kinds of aircraft that could prove useful in some of the close urban warfare battles between forces loyal to Gadhafi and rebels bent on his ouster.

NATO acknowledged Friday that its airstrikes had hit rebels using tanks to fight government forces in eastern Libya, saying it thought only Gadhafi regime forces had used heavy armored vehicles.

Yet if NATO did not know, that seems extraordinary: Video and photos from the start of the uprising against Gadhafi’s rule a month ago showed that some Libyan armored units had changed sides in the early stages of the rebellion, bringing their equipment with them.

On Friday, British Rear Adm. Russell Harding, deputy commander of the NATO operation, said it was difficult for allied pilots to distinguish between rebels and regime troops engaged in a series of advances and retreats between the eastern coastal towns of Brega and Ajdabiya.

“I am not apologizing (for the bombing),” Harding told reporters in Naples, Italy, where the alliance’s operational center is located. “The situation on the ground was and remains extremely fluid, and until yesterday we did not have information that (rebel) forces are using tanks.”

NATO Secretary-General Anders Fogh Rasmussen expressed regret over the rebels’ loss of life, but he too offered no apology.

A U.S.-led coalition initially launched the air war on March 19. Although the first such strikes on Libyan targets quickly destroyed most of Gadhafi’s fixed surface-to-air missile emplacements and the radars that control them, Gadhafi’s forces are believed to have hundreds of automatic cannon and shoulder-launched rockets — including sophisticated Russian-built Iglas — that can easily down planes like A-10 Thunderbolts or AC-130 gunships at low altitudes.