NATO has admitted that its forces accidentally killed at least four civilians in eastern Afghanistan, and a local official said foreign troops clashed with Afghan police in the west, killing nine. The reported civilian and police deaths could damage popular support for the Afghan government as well as for foreign forces operating here. President Hamid Karzai has pleaded with the US and other nations fighting resurgent militants to avoid civilian casualties. NATO's International Security Assistance Force said it was investigating whether three other civilians also were killed Saturday night in the Barmal district of Paktika province when its troops fired two mortar rounds that landed nearly half a mile (1 kilometer) short of their target. The alliance said it was providing medical aid to four civilians who were wounded.