unite nations unite nations secretary-general antonio guterres appeal myanmar authorities tuesday end violence rohingya muslims country rakhine state warn risk ethnic cleanse regional destabilization also urge security council press restraint calm send 15-member body rare letter express concern violence could spiral humanitarian catastrophe implications peace security could continue expand beyond myanmar border nearly 125,00 rohingya muslims flee bangladesh myanmar northwestern rakhine state since violence begin aug. 25 rohingya insurgents attack dozens police post army base ensue clash military counter-offensive kill least 400 people ask violence could describe ethnic cleanse guterres tell reporters tuesday face risk hope get appeal authorities myanmar civilian authorities military authorities indeed put end violence opinion create situation destabilize region say myanmar say security force fight legitimate campaign terrorists responsible string attack police post army since last october myanmar officials blame rohingya militants burn home civilian deaths right monitor rohingya flee neighbor bangladesh say myanmar army try force campaign arson kill u.n. security council meet behind close doors last week brief situation request britain continue deteriorate one things hold meet shine spotlight situation britain u.n. ambassador matthew rycroft say monday treatment buddhist-majority myanmar roughly 1.1 million muslim rohingya big challenge face leader aung san suu kyi accuse western critics speak minority long complain persecution rarely use article 99 u.n. charter guterres bring attention security council matter opinion may threaten maintenance international peace security guterres letter specifically involve article 99 write international community responsibility undertake concert efforts prevent escalation crisis u.n. chief warn myanmar violence could destabilize region