A US soldier has been detained in Afghanistan in connection with an incident involving civilian casualties in the southern Kandahar province, the NATO-led International Security Assistance Force (ISAF) said on Sunday.

"US Forces-Afghanistan, in cooperation with Afghan authorities, will investigate this incident," ISAF said in a statement. It did not give further details.

Kandahar Governor Tooryalai Wisa said a US soldier left his base in Kandahar on Saturday and opened fire on civilians. He said initial reports indicated up to 16 civilians were killed. That could not be immediately confirmed.