Nato planes have carried out an air strike in the Afghan province of Logar, south of the capital Kabul, with several people reported dead.
Afghan officials said 18 civilians died, including women and children.
Widespread reports of civilian deaths during air strikes often draw angry criticism from Afghan officials.
Separately, Nato said one of its helicopters had crashed in the east of the country, killing two service personnel.
The alliance said the cause of the crash was under investigation.
Sensitive issue
Tribal elders and officials in Logar told the BBC that top Taliban commanders had gathered at a house in a remote village in the district of Baraki Barak.
Afghan and Nato forces surrounded the house and warned the Taliban to surrender, but came under intense fire.
Nato forces then called for an air strike.
According to Afghan intelligence officials, the strike killed 18 civilians, including women and children who were in the houses at the time.
At least eight Taliban commanders were also killed.
A statement from Isaf, Nato's Afghan operation, confirmed much of the account. But it did not mention civilian deaths.
"While conducting a follow-on assessment, the security force discovered two women who had sustained non-life-threatening injuries," the statement said.
"The security force provided medical assistance and transported both women to an Isaf medical facility for treatment."
A Nato spokesman said later he could not confirm or deny reports of civilian deaths.
The BBC's Bilal Sarwary in Kabul says the issue of civilian casualties at the hands of Nato is highly sensitive.
Afghan President Hamid Karzai has issued several warnings to the Nato-led mission that killing Afghan civilians, even by accident, is unacceptable.
