Eight civilians and four policemen were killed in two separate roadside bomb blasts in Afghanistan on Tuesday, officials said. One woman, a child and six men were killed when the blast hit a bus in Del Aram district of western Farah province, said deputy provincial governor Mohammad Younus Rasuli The blast occurred on a road where Afghan and foreign troops have come under similar attacks and ambushes by Taliban insurgents in recent months, he told Reuters. Four policemen were killed and three others wounded in the second explosion which hit their vehicle in Logar province south of Kabul, a provincial official said. In another incident on Tuesday, U.S.-led troops killed several Taliban militants in an operation in Helmand province in the south, the U.S. military said in a statement. Some 13,000 people, including more than 370 foreign troops, have been killed during this period.