NATO forces killed four civilians and wounded three others when they fired at a vehicle that did not stop at a checkpoint in Afghanistan's volatile south, the alliance said. Civilian casualties are a sore point between Afghanistan's government and international forces operating here. President Hamid Karzai has implored NATO and US-led coalition troops to avoid killing civilians because it undermines support for his already weak central government. The latest incident occurred Saturday in the Sangin district of Helmand province in the south, the hub of the resurgent Taliban militant movement. A NATO statement said the vehicle was directed to stop but drove on. NATO forces fired warning shots away from the vehicle but were "forced to fire at it when it refused to stop, fearing an insurgent attack," it said. NATO medical personnel tended to the wounded civilians, including taking them by helicopter to a hospital, it said. The bodies of the dead were taken to their village by two civilians who were not hurt during the encounter.