NATO-led troops killed four Afghan civilians and wounded three more when their vehicle failed to stop at a checkpoint in the southern province of Helmand on Saturday, the NATO force said.

Public anger over civilian deaths has grown after a string of incidents by international troops in the past month that Afghan officials say have killed more than 60 ordinary Afghans.

The vehicle was directed to stop as it approached a checkpoint in the Sangin district of Helmand province but drove on, the International Security Assistance Force (ISAF) said in a statement.

"ISAF soldiers fired warning shots in a safe direction away from the vehicle, but were eventually forced to fire at it when it refused to stop, fearing an insurgent attack," it said.

Most ISAF troops in Helmand are British.

"ISAF deeply regrets this unnecessary incident caused by the reckless actions of the vehicle driver. The incident will be investigated," it said. More than 250 Afghan civilians were killed by Afghan and foreign forces in the first six months of this year, the United Nations says. Most of these deaths are caused by air strikes.

Taliban attacks and suicide bombs have killed far more.

The Afghan government and its allies must try harder to combat weakening public support and alienation caused by civilian casualties which the Taliban exploit through their media, the International Crisis Group think-tank said in a report on Thursday.