(Adds U.N. Security Council call for end to violence)
By Michelle Nichols
UNITED NATIONS, Sept 13 (Reuters) - U.N. Secretary-General Antonio Guterres and the U.N. Security Council on Wednesday urged Myanmar authorities to end violence against the majority-Buddhist country's Rohingya Muslims that has forced some 400,000 people to flee to Bangladesh.
Guterres said the situation in Myanmar's western state of Rakhine was best described as ethnic cleansing.
"When one-third of the Rohingya population had to flee the country, could you find a better word to describe it?" he told a news conference.
"I call on the Myanmar authorities to suspend military action, end the violence, uphold the rule of law, and recognize the right of return of all those who had to leave the country," said Guterres, adding that he had spoken several times with Myanmar's national leader, Aung San Suu Kyi.
The exodus of refugees, sparked by the security forces' fierce response to a series of Rohingya militant attacks on Aug. 25, is the most pressing problem Suu Kyi has faced since becoming leader last year.
The government says it is targeting "terrorists," while refugees say the offensive aims to push Rohingya out of Myanmar.
The 15-member Security Council met behind closed doors on Wednesday, at the request of Sweden and Britain, to discuss the crisis for the second time since it began and agreed to publicly condemn the situation.
The council "expressed concern about reports of excessive violence during the security operations and called for immediate steps to end the violence in Rakhine, de-escalate the situation, re-establish law and order, ensure the protection of civilians ... and resolve the refugee problem."
British U.N. Ambassador Matthew Rycroft said it was the first statement from the Security Council on Myanmar in nine years. Such statements have to be agreed by consensus and Russia and China have traditionally protected Myanmar from any action.
Myanmar said last week it was negotiating with Russia and China to ensure they blocked any censure by the Security Council over the violence in Rakhine state.
The United Nations' top human rights official earlier this week denounced Myanmar for conducting a "cruel military operation" against the Rohingya, branding it "a textbook example of ethnic cleansing."
Suu Kyi has canceled a trip to the U.N. General Assembly in New York next week to deal with the crisis. Rycroft said two high-level meetings on Myanmar were due to be held during the gathering of world leaders at the United Nations.
"The humanitarian situation is catastrophic," Guterres said. "This is a dramatic tragedy. People are dying and suffering in horrible numbers and we need to stop it."
(Reporting by Michelle Nichols; Writing by Eric Walsh, Editing by G Crosse and Steve Orlofsky)
International pressure has been growing on Buddhist-majority Myanmar to end the violence in the western state of Rakhine that began on Aug. 25 when Rohingya militants attacked 30 police posts and an army camp.
The raids triggered a sweeping military counter-offensive against the insurgents, whom the government labels terrorists. Refugees say the offensive is aimed at pushing Rohingya out of Myanmar.
Numerous Rohingya villages in the north of Rakhine state have been torched but authorities have denied that security forces or Buddhist civilians have been setting the fires. Instead, they blame the insurgents.
In the latest violence reported by the government, the insurgents attacked and burned three police posts in the north of Rakhine on Tuesday. There were no reports of casualties.
The Trump administration has called for protection of civilians, and Bangladesh says all the refugees will have to go home and has called for safe zones in Myanmar. Zaw Htay said safe zones were not acceptable.
China, which competes with the United States for influence in Asia, said on Tuesday it backed Myanmar's efforts to safeguard "development and stability".
The U.N. Security Council is to meet on Wednesday behind closed doors for the second time since the crisis erupted. British U.N. Ambassador Matthew Rycroft said he hoped there would be a public statement agreed by the council.
Myanmar's military, which ruled for almost 50 years until it began a transition to democracy in 2011, retains significant political powers and has full control of security.
Nevertheless, critics say Suu Kyi could speak out against the violence and demand respect for the rule of law.
But anti-Rohingya sentiment is common in Myanmar, where Buddhist nationalism has surged since the end of military rule.
Suu Kyi, whom the military blocked from becoming president and who says Myanmar is at the beginning of the road to democracy, could risk being denounced as unpatriotic if she were seen to be criticising a military operation that enjoys widespread support.
A mob in central Myanmar threw stones at Muslim shops on Sunday but there have been no serious outbreaks elsewhere.
Zaw Htay said the government had information about plots to launch attacks, although he did not elaborate, except to say security was being tightened in cities.
Those fears will be compounded by an al Qaeda call to arms in support of the Rohingya.
"The savage treatment meted out to our Muslim brothers ... shall not pass without punishment," al Qaeda said in a statement, the SITE monitoring group said.
Bangladesh was already home to about 400,000 Rohingya who fled earlier conflict and many of the new refugees, hungry and sick, are without shelter or clean water.
"We will all have to ramp up our response massively, from food to shelter," George William Okoth-Obbo, assistant high commissioner for operations at the U.N. refugee agency, told Reuters during a visit to the Kutupalong camp in Bangladesh.
He declined to say how many people he thought might come but Bangladeshi officer Lieutenant Colonel Ariful Islam said numbers were falling off sharply in his area.
"The people who arrived in the early days after the atrocities, now they've come out," Islam told Reuters.
(Additonal reporting by Krishna D. Das and Simon lewis in Bangldesh, Kanupriya Kapoor in JAKARTA; Writing by Robert Birsel; Editing by Simon Cameron-Moore and Clarence Fernandez)