Scores of civilians have been killed during Nato operations against Taleban fighters in southern Afghanistan, local officials and civilians say.
Nato said it had "credible reports" of civilian casualties in two districts of Kandahar province, but could not confirm that as many as 60 had died.
Spokesman Mark Laity said 48 militants had been killed, and apologised for any inadvertent civilian deaths.
The UN Afghan mission said it was seriously concerned about the incident.
Mr Laity told the BBC the alliance would help Afghan officials investigate what happened.
He said that militants in the area sometimes used civilians as human shields.
"When you have active insurgency, things can happen," Mr Laity said.
"We've got an active insurgency down here. We've got tight rules of engagement but sometimes things go wrong."
"Sometimes the Taleban are among local people, sometimes there aren't civilians - the Taleban claim there are civilians and there aren't."
Locals in Panjwayi and Pashmul districts of Kandahar province say the Nato raids began on Tuesday, during the Eid al-Fitr festival marking the end of Ramadan, and continued into the night.
They said that several houses were hit, and civilians killed.
Funerals have already been held for a number of those killed, relatives said.
Villagers told the BBC Pashto service that the bodies of many locals had been pulled from the rubble of their homes after the raids and buried.
"Twenty members of my family are killed and 10 are injured," one survivor said. "The injured are in Mirwais hospital in Kandahar city and anybody can go and see them.
"For God's sake, come and see our situation."
Another man said women and children were among 15 members of his family who had been killed.
"The airplanes came and were bombing until 3 am. And, in the morning, they started hitting our village with mortars and rockets. They didn't allow anybody to come to our help."
Afghan Interior Ministry spokesman Zmarai Bashiry told the BBC that local police and officials had confirmed more than 40 villagers killed in the Nato raids.
Other local officials put the death toll at between 60 and 85.
'Sorry not enough'
A statement from President Hamid Karzai said an eight-member team of tribal and community elders would investigate the reported civilian casualties.
Nato says it routed the Taleban in battles in September
The elders would also make suggestions on how to prevent such "unfortunate" incidents in future and ensure better co-ordination with foreign forces.
A Taleban statement sent to the BBC said none of the movement's fighters had been killed in the Panjwayi clashes, and that any deaths were civilian.
President Hamid Karzai has been under mounting pressure over civilian deaths and has urged foreign forces to exercise more caution.
Last week, up to 21 civilians were killed in two Nato operations in Kandahar and neighbouring Helmand province.
Hundreds of people have been killed in Afghanistan this year, the bloodiest since the Taleban were removed from power by US-led forces in 2001.