Two tribal elders were killed in an insurgent attack in southern Afghanistan, where three police troops were killed in a roadside bombing, officials said Monday. Niaz Mohammad Sarhadi, chief of the Zherai district in Kandahar province, said he and a group of tribal elders were inspecting some reconstruction projects when Taliban fighters attacked their convoy. Two tribal chiefs were killed and four others were injured, Sarhadi said. Three policeman were killed and one injured by a roadside bomb in Nad Ali district of neighboring province of Helmand on Sunday, the Interior Ministry said. Four civilians were injured Monday when a bomb loaded on a motorbike was detonated in the centre of Khost city, the provincial capital of the province of the same name, the ministry was quoted as saying by the German Press Agency "DPA".