An American soldier walked into a village near his base in southern Afghanistan, and shot and killed at least 15 civilians early Sunday morning, The Wall Street Journal reported.
Another five Afghan civilians were injured, the paper said. Nine children and three women were reportedly among the victims.
The unnamed soldier turned himself in to US military officials later Sunday and may have suffered some type of mental breakdown, the BBC said.
According to the Associated Press, President Hamid Karzai called the incident an "assassination," and demanded an explanation from Washington.
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The US military in a statement to the BBC said it had detained one of its own service members after what it called “a deeply regrettable incident." The US said it was investigating the shooting, but gave no other details.
A NATO spokesman told the Associated Press it was unclear whether the shooter knew the victims.
The shooting occurred in a house near the base where the soldier was stationed in Kandahar, in the country's south. An area resident told The New York Times the shooting happened Saturday at the home of an area tribal elder.
The shooting comes after a series of violent incidents between Afghan soldiers and American troops at a particularly tense time following an incident where several US soldiers were found to be burning copies of the Quran at Bagram Air Base.
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