Two civilians were among ten people killed in a US-led coalition operation in western Afghanistan on Friday, the US military said, the latest in a mounting toll of civilian deaths that has outraged Afghans. The military said fighting erupted after coalition and Afghan army troops were ambushed by militants during a reconnaissance patrol in Farah province. Troops backed by close air support killed six militants, it said in a statement. "Two civilians were killed and two wounded during the conduct of the insurgent ambush operation." An Afghan army commander earlier told Reuters that a woman and a child were killed in the air strike by coalition planes. The latest deaths come at a time of simmering anger over civilian casualties, which has also opened up a rift between the US-led coalition and the Afghan government. More than 500 civilians have been killed during operations by foreign and Afghan forces against the militants so far this year, according to the Afghan government and some aid groups. The Farah airstrike was aimed at the house of a local Taleban commander who was among those killed, said Ghulam Farouq Niami, an Afghan army commander for the western zone. Farah province adjoins Herat, where the Afghan government says more than 90 civilians were killed in a coalition air strike last month, figures supported by the United Nations. The US military disputes that figure and a three-way investigation involving the United Nations has been proposed. Western military officials say Taleban fighters deliberately use civilians as cover, drawing coalition firepower against non-combatants in an attempt to reap propaganda gains. Separately, the US army said troops had killed several militants in an operation in northern Kapisa province on Friday. Violence has surged in Afghanistan this year as the hardline Taleban have stepped up their campaign of guerrilla attacks backed by suicide and roadside bombs to oust the pro-Western Afghan government and drive out foreign troops. Meanwhile, more foreign soldiers were killed in Afghanistan during August than in any other month since the 2001 US-led invasion, an independent website said, reflecting a rise in Taleban attacks. Forty-three foreign soldiers were killed in combat in August, five more than in June, the second highest month, according to icasualties.org, an independent website that tracks troop casualties in Afghanistan and Iraq.