Afghan officials say a mortar round explosion near the main U.S. air base in Bagram has killed one Afghan civilian and wounded two others.

Local authorities say Thursday's blast occurred several hundred meters from the gates of the Bagram air field, north of the capital, Kabul. There were no American casualties.

In a separate incident, in southern Helmand province, Afghan police mistakenly opened fire on coalition soldiers, prompting a shootout that wounded eight policemen.

The incident comes two days after U.S.-led coalition forces began investigating whether an American and a Canadian soldier killed in a battle against Taleban rebels last week were victims of friendly fire. Five coalition troops - an American, three Canadians and one Afghan - also were wounded in the incident.

Some information for this report was provided by AFP, AP and Reuters.