A Nato air strike has killed 14 people, all civilians, in south-west Afghanistan's Helmand province, local officials say.
The strike took place in Nawzad district after a US Marines base came under attack on Saturday.
The air strike, targeted at insurgents, struck two civilian homes, killing two women and 12 children, reports say.
Afghan President Hamid Karzai has called on the US military to avoid operations that kill civilians.
"The president called this incident a great mistake and the murdering of Afghanistan's children and women, and on behalf of the Afghan people gives his last warning to the US troops and US officials in this regard," his office said.
The White House said it was taking Mr Karzai's concerns "very seriously".
Nato and Afghan troops are looking into the incident.
A group from Sera Cala village travelled to Helmand's capital, Lashkar Gah, bringing with them the bodies of eight dead children, some as young as two years old, says the BBC's Quentin Sommerville in Kabul.
"See, they aren't Taliban," they chanted as the carried the corpses to local journalists and the governor's mansion.
Earlier, a coalition soldier was killed in a gun battle with insurgents in the area and an air strike was called in, said a spokesman for the international mission.
While insurgents are responsible for most civilian deaths in Afghanistan, the killings of Afghans by foreign soldiers is a source of deepening anger, our correspondent adds.
President Hamid Karzai has criticised Nato for not doing enough to prevent such deaths, especially during "night raids" and has called on the country's ministry of defence to stop what he described as "arbitrary" operations by foreign forces.
Nuristan 'air strike'
Separately, 20 Afghan police and 18 civilians were killed on Wednesday in a Nato air strike in north-eastern Afghanistan, in which some 30 Taliban fighters were also killed, the governor of the province of Nuristan has told the AFP news agency on Sunday.
The police and civilians were targeted Wednesday after they were mistaken for militants, the governor said.
Nuristan was the scene of heavy battles last week between the Taliban and Afghan security forces.
"The policemen were killed due to friendly fire," Jamaluddin Badr told AFP, adding the air strike in the troubled district of Doab targeted a location that the officers "had just" taken from the insurgents during fighting.
"Civilians were killed because the Taliban... [who] ran out of ammunition fled into the civilians' houses and then the civilians were mistaken with the Taliban and fired upon," the governor said.
The Nato-led International Security Assistance Force has said it is investigating the allegations. A spokesman told AFP agency that its initial results showed civilians were not involved.
In the country's north, security was extremely tight for the funeral of Gen Mohammad Daud Daud, the police commander for northern Afghanistan who was killed in a suicide bomb attack on the provincial governor's compound in Takhar on Saturday.
He was one of at least six people killed in the attack, which was claimed by the Taliban.