NATO says an alliance helicopter crew has killed more than 20 insurgents in southern Afghanistan after the men fired on the aircraft.

The statement says a group of fighters shot at the helicopter with small arms and machine guns before the crew returned fire.

It says a ground team found 20 bombs, firearms and several vehicles.

NATO says initial reports show there were no civilian casualties during Thursday's fighting in the Spin Boldak district of Kandahar province.

The coalition tightened its rules of engagement last year after complaints its air raids frequently killed civilians instead of insurgents.

Reports of civilian deaths caused by NATO have dropped by a third.
NATO and Afghan forces began pushing into the insurgency's heartland in southern Afghanistan in July.