Suspected separatist insurgents have killed three people in Thailand's turbulent south, beheading one of the victims in the fourth such incident in a week, police said Thursday. A group of rebels shot dead a 36-year-old army ranger and his 21-year-old relative in Narathiwat province late Wednesday, police said, before beheading the younger victim and mutilating both corpses with a knife. Two soldiers and a civilian have been killed and beheaded in similar attacks in the south since last Friday, as militants step up a tactic aimed at terrifying villagers so they do not inform authorities, officials say.