A US soldier has reportedly killed at least three civilians and injured several, in Kandahar, Afghanistan on Sunday.

The governor of Kandahar province said initial reports indicated that three people were killed, reported AFP.

"Our initial information indicates that three people are dead but we don't know who they are," AFP quoted Governor Toryalai Wesa as saying.

The US soldier is said to have had a breakdown before leaving his military base and firing at civilians, according to BBC reporter Quentuin Sommerville in Kabul.

Nato-led International Security Assistance Force (Isaf) in a statement confirmed that the US soldier was detained in connection with the incident, reported AFP.

"US forces, in cooperation with Afghan authorities, will investigate the incident," Isaf said.

"This is a deeply regrettable incident and we extend our thoughts and concerns to the families involved," the statement read.

Anti-US protests have already been on the rise in Afghanistan after an incident involving US soldiers burning the Koran erupted into violent protests killing some 40 people in February.