A US soldier in Afghanistan has shot dead 16 civilians and wounded others after entering their homes in Kandahar province, Afghan and Nato sources say.
He reportedly left his base early in the morning to attack village homes. Nine children are among the dead.
The White House voiced “deep concern” and Nato-led forces in Afghanistan promised a rapid inquiry.
Afghan President Hamid Karzai has condemned the attack and demanded an explanation from Washington.
BBC correspondents say there could be a furious backlash when news of the attack reaches the wider public.