The U.S. military in Afghanistan said Tuesday a roadside bomb in southern Helmand province killed four soldiers with the U.S.-backed coalition and an Afghan civilian working with the troops.

The nationalities of the troops were not released.

Also in Helmand, Afghan National Army soldiers killed 16 militants after coming under fire during a routine patrol.

Afghan soldiers assisted by coalition forces responded first with small arms fire, then with strikes when militants began firing mortars and grenades at the patrol. The U.S. military says no non-combatants were in the area during the battle.

Meanwhile, Canada is investigating the deaths of two Afghan children Monday near the southern city of Kandahar after handling unexploded munitions reportedly left behind by Canadian troops.

A Canadian Defense Ministry said Tuesday Canadian forces have "strict policies in place that prohibit leaving behind any unexploded ordnance and make every effort to ensure the safety of Afghan civilians."

Southern Afghanistan is a stronghold of Taliban insurgents and other militants battling NATO and U.S. forces.

U.S. President Barack Obama las week approved the deployment of an additional 17,000 troops to Afghanistan to help stabilize the region. He is also conducting a policy review of the region.