 Assailants believed to be members of armed groups opposed to Somalia's transitional government and its Ethiopian allies have killed four police officers in the capital, Mogadishu, in continued fighting described by human rights organisations as mostly affecting civilians.A roadside bomb in northern Mogadishu killed three police officers and wounded a large number of civilians.At least one person was reported dead Friday in a small village in southern Somalia after tens of people rushed on a building where an aid agency was distributing food, witnesses said.