Afghan officials said at the time that three children, two boys and a girl, died in a NATO airstrike in Helmand province which targeted Taliban insurgents planting mines on a road.

The statement by NATO's International Security Assistance Force (ISAF) said the incident did not involve an airstrike, but it did not explain how the civilian deaths had occurred.

"During an operation in Helmand Province Sunday against suspected insurgents laying IEDs, ISAF forces may have accidently killed three innocent Afghan civilians," ISAF said.

"The Coalition extends its deep regret for this tragic incident. We also extend our sympathies to the families and loved ones of those who died, and we take full responsibility for what occurred."

ISAF said it would work closely with Afghan officials "to determine what happened and why" and would meet the family members of those who died to personally express regret and condolences.

Civilian casualties caused in NATO operations against insurgents are a sensitive issue in relations between the US-led force and the government of President Hamid Karzai.

Karzai often reacts angrily, arguing that such incidents turn people against his administration amid an ongoing insurgency by Taliban Islamists trying to bring him down.

Thousands of civilians are killed in the war each year, with the United Nations saying the vast majority of such deaths are caused by insurgents.