Afghan President Hamid Karzai on Friday condemned US troops for killing a four-year-old boy in the southern province of Helmand, in a fresh strain to troubled relations between Washington and Kabul.
Helmand governor Naeem Baloch told Karzai during a meeting in Kabul about the shooting, which comes as the US and Afghanistan wrangle over a deal to allow some US troops to remain in the country after this year.
The US-led Nato coalition in Afghanistan issued a statement expressing "deepest sympathies to the family who suffered the loss of a loved one" in the incident on Wednesday and vowing to investigate "what happened and why".
Relations between Washington and Kabul have been poor for years, and negotiations over the bilateral security agreement (BSA) have erupted into a long-running public dispute.
Karzai made a surprise decision not to sign the agreement promptly despite having vowed to do so, leading to the threat of a complete withdrawal of Nato troops by the end of 2014.
Civilian casualties have been one of the most sensitive issues of the 13-year military intervention in Afghanistan, and Karzai has often used accidental shootings and misguided airstrikes to berate foreign countries and stir public anger.
In a classified cable reported by the Washington Post this week, US Ambassador James Cunningham said he did not expect Karzai to agree to sign the document before the vote.