Afghan and Western officials say Afghanistan's intelligence agency and the U.N. both have video of the aftermath of the Aug. 22 U.S. airstrikes on the village of Azizabad showing dozens of dead women and children.
The Afghan government and the U.N. have said the raid killed 90 civilians, including 60 children.
The U.S. military said in a statement Sunday it will send a general officer to review the findings of the initial U.S. investigation that up to 35 militants and seven civilians died.
The BBC adds more about the nature of the new evidence.
Video footage from mobile phones showing dozens of dead bodies has given increasing credibility to claims by local residents that up to 90 civilians were killed in the attack.
The footage shows bodies - many of them women and children - lined up in a mosque in the village of Azizabad, which was the subject of a combined ground operation and airstrike by US forces.
Both the Afghan government and the United Nations have already carried out their own investigations into the attack.
They say the video evidence, and the presence of a large number of fresh graves in the village, confirm the accounts of local people.
Until now, the US military has insisted that far fewer civilians died in what it says was a successful operation against Taleban militants in the area.
On Sunday, however, the senior US commander in Afghanistan, David McKiernan, said that in light of new evidence, he had asked for the American investigation to be reopened.
You can watch some of the video as part of a BBC World news report on the incident here.
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Violence is still rising in Afghanistan, with a higher rate of US troop deaths now than Iraq even at its worse. More than more than 2,500 people, including 1,000 civilians, have been killed in the last six months and, overall, coalition forces have killed almost as many civilians as militants have. Airstrikes have been blamed for many of the deaths.
Just after the airstrike in Herat district, Afghan president Hamid Karzai visited grieving relatives and told them "I have been working day and night over the past five years to prevent such incidents, but I haven't been successful in my efforts. If I had succeeded, the people of Azizabad wouldn't be bathed in blood."