UNITED NATIONS (Reuters) - United Nations Secretary-General Antonio Guterres appealed to Myanmar authorities on Tuesday to end violence against Rohingya Muslims in the country s Rakhine state, warning of the risk of ethnic cleansing and regional destabilization.  He also urged the Security Council to press for restraint and calm, sending the 15-member body a rare letter to express concern that the violence could spiral into a  humanitarian catastrophe with implications for peace and security that could continue to expand beyond Myanmar s borders.  Nearly 125,00 Rohingya Muslims have fled to Bangladesh from Myanmar s northwestern Rakhine state since the violence began on Aug. 25, when Rohingya insurgents attacked dozens of police posts and an army base. The ensuing clashes and a military counter-offensive have killed at least 400 people.  When asked if the violence could be described as ethnic cleansing, Guterres told reporters on Tuesday:  We are facing a risk, I hope we don t get there.   I appeal to all, all authorities in Myanmar, civilian authorities and military authorities, to indeed put an end to this violence that, in my opinion, is creating a situation that can destabilize the region,  he said. Myanmar says its security forces are fighting a legitimate campaign against  terrorists  responsible for a string of attacks on police posts and the army since last October. Myanmar officials blamed Rohingya militants for the burning of homes and civilian deaths but rights monitors and Rohingya fleeing to neighboring Bangladesh say the Myanmar army is trying to force them out with a campaign of arson and killings. The U.N. Security Council met behind closed doors last week to be briefed on the situation at the request of Britain.   If it continues to deteriorate then one of the things that we can do is to hold further meetings to shine a spotlight on the situation there,  Britain s U.N. Ambassador Matthew Rycroft said on Monday. The treatment of Buddhist-majority Myanmar s roughly 1.1 million Muslim Rohingya is the biggest challenge facing leader Aung San Suu Kyi, accused by Western critics of not speaking out for the minority that has long complained of persecution. Under the rarely used Article 99 of the U.N. Charter, Guterres can  bring to the attention of the Security Council any matter which in his opinion may threaten the maintenance of international peace and security.  While Guterres  letter does not specifically involve Article 99, he writes that  the international community has a responsibility to undertake concerted efforts to prevent further escalation of the crisis.  
U.N. chief warns Myanmar violence could destabilize region