Afghan authorities say security forces in southern Helmand province have shot and killed four suspected Taleban insurgents planting land mines intended for counter-narcotics forces.

Helmand is Afghanistan's largest grower of opium poppies and a hotbed of insurgent activity.

In other violence Tuesday, in neighboring Nimroz province, unidentified gunmen shot dead a district intelligence officer as he was driving in his car.

Meanwhile, U.S.-led coalition forces in Afghanistan say they are 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 battle in Helmand province.

The U.S. military says coalition troops killed 32 Taleban insurgents in the operation.

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