LASHKAR GAH, Afghanistan - Afghan officials said Sunday that NATO-led troops killed 14 civilians, all of them women and children, in the southern province of Helmand on Saturday night.
It was one of the deadliest foreign assaults on civilians in Afghanistan in months.
The commander of the NATO-led International Security Assistance Force (ISAF) in southwestern Afghanistan apologised for the deaths of civilians, saying troops had unwittingly targeted a home because insurgents were using it as a base.
"Unfortunately, the compound the insurgents purposefully occupied was later discovered to house innocent civilians," Major General John Toolan said in a statement.
"While I know there is no price on human life we will ensure that we make amends with the families in accordance with Afghan culture," he added.
The governor of Helmand province said the bomb killed 14 civilians, two of them women and the remainder children. Bereaved relatives brought the bodies of young children to the provincial capital to protest.
ISAF did not give the ages of the civilians it said died.
Karzai condemned the latest case of civilian casualties from NATO air strikes, saying he had warned US and NATO troops their "arbitrary and unnecessary operations" were killing innocent people "every day".
He said in a statement the incident in violent Helmand province in the south was "a big mistake".
"It shows that attention is not being paid," he said.
The White House shares Karzai's concerns over civilian casualties, and takes them very seriously, US President Barack Obama's spokesman said after the air strike.
"WHY WAS MY HOUSE BOMBED?"
Both the Helmand governor and Toolan said coalition troops had come under fire -- and Toolan said one US Marine was killed -- before they ordered the bombing of a compound where the insurgents had taken shelter.
The Helmand governor said in a statement that seven boys and five girls were among the dead and three other children wounded.
Bereaved male relatives cradled the bodies of several young children wrapped in bloody sheets and placed side to side, and brought them in the back of a truck to the provincial capital, Lashkar Gah, Reuters television pictures showed.
"My house was bombarded in the middle of the night and my children were killed ... the Taliban were far away from my home, why was my house bombed?" relative Noor Agha said.
The NATO air strike comes at a time of high anti-Western sentiment in Afghanistan and days after deadly protests by thousands of people against a night raid by NATO troops in which four people, including two women, were killed.
Twelve people were killed during those violent protests and clashes with police in Takhar and more than 80 wounded.
On Saturday, Karzai ordered the Defence Ministry to take control of night raids, saying Afghan troops should be carrying out the sensitive operations themselves.
Critics of the raids, carried out on houses suspected of harbouring insurgents, say they often lead to civilian casualties as ordinary people rush to defend their homes.
Under a plan agreed by NATO leaders, foreign troops will begin handing over security responsibilities to Afghan troops from July, with a plan to withdraw all combat troops from Afghanistan by the end of 2014.
Despite the presence of some 150,000 foreign troops, violence in Afghanistan last year reached its deadliest phase since US-backed Afghan forces toppled the Taliban in 2001.
The Taliban this month announced the start of their "spring offensive", vowing to attack foreign and Afghan troops and government officials.
NATO air strike kills civilians, mostly children