International forces in Afghanistan say they are urgently investigating reports as many as 45 civilians died in an air strike in Helmand province on Friday.
Nato's initial investigation found no evidence, but a BBC journalist visiting Regey village spoke to several people who said they had seen the incident.
At the time, dozens were sheltering in the village from nearby fighting.
A significant civilian loss of life would be rare this year as a new policy of restraint has reduced casualties.
Witnesses said the attack had come in daylight as dozens sheltered from fighting in nearby Joshani.
Mohammed Khan, a boy aged about 16, said helicopters had circled over the village before the incident. He said that he had warned other children to take cover.
But his mother told him not to worry them. He went further away and was shielded by a wall that saved his life when the attack started.
"I heard the sound of the rocket land on our house. I rushed in screaming with my father and saw bodies lying in the dust… I found I was even standing on a dead body."
One of the bodies was his brother.
"He had been lying asleep in the afternoon when they were killed," Mohammed said.
After the attack relatives and neighbours came to assist in digging out the dead and taking the injured to hospital.
Sher Mohammed said that the owner of the house had been his cousin. He said it had taken until late into the night to dig out the bodies. Rescuers buried 39 and believed six were left under the rubble, he added.
The bodies were buried at daylight. Haji Rahim could not contain his tears. He said that after a sleepless night, he and other villagers had gone to talk to a Nato patrol.
He said: "They can see something as small as an insect just four inches on the ground, so how were they not able to see all of those women and children when they bombed them?"
For several months there has been a significant reduction in civilian casualties and very few air strikes under a new policy of restraint ordered by Gen Stanley McChrystal.
He was forced from his post recently after talking too frankly to journalists.
A spokesman for the international forces, Lt Col Chris Hughes, said: "A preliminary investigation by [Nato's] Isaf forces and the provincial governor, which included a meeting with local elders, gives no indication of a mass casualty incident caused by coalition forces in Sangin."
But he added: "We take allegations of civilian casualties very seriously. We go to great measures to avoid civilian casualties in the course of operations. The safety of the Afghan people is very important to the International Security Assistance Forces."