Afghan officials: U.S. missiles killed 27 civilians

"The wedding participants were on their way to the groom's house," Wazir said outside the hospital, his tunic covered in blood after carrying some of those wounded.

"They stopped in a narrow location for rest. The plane came and bombed the area. There were between 80 to 90 people altogether. We have carried six of the injured to this hospital, and more might be coming. The exact number of casualties is not clear," he said.

A U.S.-led coalition statement said an airstrike killed several militants in Nangarhar.

The issue of civilian casualties has caused friction between the Afghan government and U.S. and NATO troops, and has weakened the standing of Western-backed Karzai in the eyes of the population.

Karzai has repeatedly called for better coordination between Afghan and foreign troops in pursuing militants through populated areas, and for international troops to cut down on civilian casualties. Deaths of ordinary Afghans caused a huge outcry last year, but there have been fewer accusations of such killings in recent months.

McKiernan said NATO uses a "very judicious and strict application of lethal force."

"Civilian casualties are very, very important in this campaign. One is one to many," he said. "I do think we have ... the right procedures in place to mitigate and minimize any collateral damage to people or material."

Perry said Sunday that military reports still indicated that the Friday airstrike by coalition helicopters in Nuristan hit two vehicles carrying militants who had attacked a NATO base with mortars.

Karzai suggested that Afghan civilians may have been fleeing at the time of the strike because of a warning from the U.S. coalition.

"Coalition forces are saying that this operation was against armed insurgents in the area, but Gov. Nuristani is insisting that three hours before this airstrike, people were informed by international forces that they should leave the area because of a possible airstrike against insurgents," Karzai said in a statement.

Elsewhere, in the southern province of Helmand — the country's other hotly contested region — a clash killed seven Taliban and two police, provincial police Chief Mohammad Hussein Andiwal said. Five other officers were wounded during the Saturday fight in Nawa district, he said.

The coalition said several militants were also killed Friday during an operation in Ghazni province.

More than 2,100 people — mostly militants — have been killed in insurgency-related violence in Afghanistan this year. More than 8,000 people died in attacks last year, according to the U.N., the most since the 2001 U.S.-led invasion.

The number of militant attacks has been on the rise this summer compared with the same period last year, NATO officials say.