A US soldier in Afghanistan is reported to have killed at least three Afghan civilians after walking off his base in Kandahar province.
The soldier then surrendered to the US military authorities.He is believed to have suffered a mental breakdown.
A US military statement said a service member had been detained after "a deeply regrettable incident".
The statement gave no details of the incident itself but said it was under investigation.
The statement added: "This is a deeply regrettable incident and we extend our thoughts and concerns to the families involved."