The Nato-led Isaf force has apologised for the deaths of two Afghan boys, killed when a helicopter fired on them, mistaking them for insurgents.
The boys, aged under seven, were killed on Thursday in Uruzgan province.
Isaf takes "full responsibility for this tragedy", its commander said.
Analysts say civilian deaths enrage the Afghan people and President Hamid Karzai, who recently stopped his troops calling in foreign air strikes in built-up areas.
That move came after a 13 February incident where a Nato air strike requested by Afghan forces killed 10 people, including five women and four children.
In a statement on Saturday, Gen Joseph Dunford said: "I offer my personal apology and condolences to the family of the boys who were killed."
He said that the boys - who were tending cattle - "were killed when coalition forces fired at what they thought were insurgent forces".
"I am committed to ensuring we do the right thing for the families of those we harmed, as well as for the community in which they lived," the statement added.
Gen Dunford added that Isaf and Afghan investigators had already visited the village in the central province where the boys lived and met local leaders.
The AFP news agency reported that it was Australian troops who shot the boys, after coming under attack from the Taliban in that area.
The governor of Uruzgan, Amir Mohammad Akhundzada, was quoted by AFP as saying: "The children were killed by Australian troops, it was a mistaken incident, not a deliberate one."
Australian forces, who are deployed in Uruzgan, were involved in an "operational incident" in the province, Australian parliamentary Secretary for Defence David Feeney said on Friday.
He added that the Australian military and the Isaf were investigating the incident.
About 1,500 Australian soldiers are based in Uruzgan province. Their main focus is to provide training and mentoring to Afghan soldiers.
President Karzai has demanded time and time again that Nato-led forces take more care and prevent such incidents from occurring, the BBC's Quentin Sommerville in Kabul, says.
The Isaf (International Security Assistance Force) has reduced the number of such killings, but they keep happening, our correspondent adds.
The Nato-led troops are scheduled to withdraw from Afghanistan by the end of 2014 and have gradually been handing over responsibility for security to Afghan counterparts.
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