**At least four civilians were killed and 18 others wounded when Nato forces fired at a bus in southern Kandahar province, Afghan officials say.**The bus was travelling from Kandahar to western Herat province on Monday morning, provincial officials said.
Nato said it was aware of the incident and had sent a team of investigators, the AFP news agency reported.
Civilian deaths at Nato hands is the source of increasing friction between the Afghan government and Nato.
Last week Nato admitted its forces were responsible for the deaths of three women during a botched night-time raid in eastern Afghanistan in February.
And it is also investigating whether its forces killed four civilians on an air strike in southern Helmand province in early April.
Nato and Afghan forces are currently engaged a massive anti-Taliban operation to rid parts of southern Helmand province of militants.
Nato officials have indicated that the offensive will switch focus to Kandahar in the coming months.
Since taking up his position as top commander in Afghanistan, General Stanley McChrystal has said reducing civilian casualties is a key priority for Nato.
He has introduced changes to Nato tactics aimed at cutting the risks to civilians. Measures include reducing the number of air strikes and night raids.This article is from the BBC News website. © British Broadcasting Corporation, The BBC is not responsible for the content of external internet sites.