“Those who succeeded in reaching the trenches were killed when the trench collapsed after it was hit by rockets or bombs being fired from coalition helicopters,” he said. “Those who were on their way to the trench were killed by rockets or bullets. I visited the trench. I saw old, dried blood. I saw women and children’s garments. I saw blood-stained walls of the trench. I saw pieces of blankets and cotton from the quilts the villagers wrapped themselves in because of the cold weather.”

However, the discrepancy in how many graves Mr. Mulk saw versus the number of people the government reported had been killed points to some of the difficulties in assessing civilian casualties. It can be difficult to tell whether graves are new or old, or recently dug up to appear fresh, human rights organizations said. The same is true of blood stains. Similarly, the number of graves often does not correspond to the number of bodies, since there can be several bodies in a grave.

NATO, in its initial public statements last week, said that video of the assault showed armed men meeting and then dispersing on a mountainside. A NATO spokesman, Rear Adm. Gregory J. Smith, said that he saw no sign that civilians or civilian houses were attacked, although he did not rule out the possibility of civilian casualties.

NATO has acknowledged that seven to nine civilians were wounded.

Admiral Smith also said that NATO had recorded conversations among the militants discussing the idea of reporting civilian casualties to the local authorities so that they would ask NATO to stop shooting.

The NATO videos and sound recordings have not been played to reporters, making any inferences difficult to assess independently. The Afghan investigators did not see or hear the recordings, Mr. Shahzada said.

In Kandahar on Sunday, at least eight people were killed, two of them police officers, when a bomb exploded in the midst of a dogfight, a favorite spectator sport in the area and one that attracts many local commanders and police officers. The bomb is believed to have been set by the Taliban, who banned dogfighting when they controlled the government.

“For the last few months, dogfighting took place here in this field,” said Agha Jan, a tribal elder. “But today the police were all around and some old police commanders were attending the festival and police were securing the area, so Taliban knew that the police commanders were at the dogfight, so that’s why it was targeted.”