At least four civilians were killed and six others were injured in a bomb blast in the southern Helmand province of Afghanistan on Monday, locals officials said. The incident happened in Marja district when the vehicle they were traveling in hit a roadside bomb, provincial police chief Abdul Nabi Elham was quoted by Afghan Pajhwok news agency as saying. No group claimed responsibility for the blast. Insurgents use improvised explosive devices to target Afghan and NATO troops, but most of the victims are civilians who are unwittingly caught in the blast. In a separate incident, two policemen were killed and one was injured in a roadside bomb blast in the southern Uruzgan province today morning. The blast took place at about 10:00 am local time in the provincial capital Tarinkot when a police vehicle was struck by a roadside bomb, provincial police chief spokesman Farid Ayel said.