A U.S. military spokeswoman did not respond to an e-mail seeking comment.

Villagers had gathered for a memorial ceremony in Azizabad to honor a tribal leader named Timor Shah, who had allegedly been killed by Tawakil, the rival tribesman, about eight months ago. Villagers said families had traveled to Azizabad for the ceremony, one of the reasons so many children were killed.

The top NATO spokesman in Afghanistan, Brig. Gen. Richard Blanchette, has said the U.S. coalition, U.N. and Afghan government would hold a joint investigation, but Hamidzada said the Afghan government would not take part.

"The Afghan government did not agree to a three-way investigation, because we have already completed two investigations," he said.

"There is no need to go around to the village and actually harass people one more time and remind them of the terrible ordeal they went through. We have the facts straight, we have all the information."

Karzai has long pleaded with international forces to reduce the number of civilians killed in operations, and now the government is studying its "status of force" agreement governing U.S. and NATO operations in the country. Afghan officials are also reviewing the use of airstrikes by international forces.

Hamidzada said Azizabad strained a relationship between friends.

"We can be critical of one particular issue but we are still partners," he said, adding there are ways of killing Taliban without hurting civilians.

"If we only rely on air raids, we know these are not accurate, we know the potential for civilian casualties is extremely high," he said. "So there has to be a combination of ground forces and the use of Afghan military forces. But you cannot just conduct operations from the air alone, because you hurt civilians."

In violence Sunday, a suicide car bomber attacked a convoy carrying Afghan doctors working for the United Nations in southern Afghanistan, killing two doctors and their driver, officials said.

The U.N. said it was trying to determine whether the bombing was an explicit attack on the world body or if the doctors were a target of opportunity.

Also in the Afghan south, a British soldier was killed in an explosion on Saturday, the Ministry of Defense said.

Elsewhere, seven children died after ordnance they were playing with exploded, and militants ambushed and killed seven police, officials said.