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COX‘S BAZAR, Bangladesh/UNITED NATIONS — More than 60 Rohingya Muslim refugees from Myanmar are believed to have drowned when their boat capsized, the latest victims in what the United Nations says is the world’s fastest-developing refugee emergency.

The refugees drowned in heavy seas off Bangladesh late on Thursday, part of a new surge of people fleeing a Myanmar military campaign that began on Aug. 25 and has triggered an exodus of more than half a million people.

International anger with Myanmar over the crisis is growing.

In New York, U.S. Ambassador to the United Nations Nikki Haley called on countries to suspend providing weapons to Myanmar over the violence.

It was the first time the United States had called for punishment of Myanmar’s military, but she stopped short of threatening to reimpose U.S. sanctions which were suspended under the Obama administration.

Buddhist-majority Myanmar rejects accusations of ethnic cleansing and crimes against humanity and has denounced rights abuses.

Its military launched a big offensive in response to coordinated attacks on the security forces by Rohingya insurgents in the north of Rakhine State on Aug. 25.

United Nations Secretary-General Antonio Guterres told the Security Council the violence had spiraled into the “world’s fastest-developing refugee emergency, a humanitarian and human rights nightmare.”

Aid groups now say 502,000 refugees have arrived in Bangladesh since late August.

A Rohingya Muslim refugee mourns beside the bodies of his three children at a school near Inani beach in Cox's Bazar district on Friday. Fred Dufour / AFP - Getty Images

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The refugee boat that capsized went over as darkness fell, in driving wind and rain and high seas.

An official with the International Organization for Migration said 23 people were confirmed dead and 40 were missing. Seventeen survived.

“We’re now saying 40 missing, which suggests the total fatality rate will be in the range of 63,” the official, Joe Millman, told a news briefing in Geneva.

One survivor, Abdul Kalam, 55, said his wife, two daughters and a grandson were among the dead.

Kalam said armed Buddhists had come to his village about a week ago and taken away livestock and food. He said villagers had been summoned to a military office and told there were no such people as Rohingya in Myanmar.

After that he decided to leave and headed to the coast with his family, avoiding military camps on the way.

A destroyed boat is seen on a beach washed up after it sunk in rough seas off the coast of Bangladesh carrying over 100 people. Paula Bronstein / Getty Images

'Brutal campaign'

In a sharp ramping up of the pressure on Myanmar, Haley echoed U.N. accusations that the displacement of hundreds of thousands of people in Rakhine State was ethnic cleansing.

“We cannot be afraid to call the actions of the Burmese authorities what they appear to be - a brutal, sustained campaign to cleanse the country of an ethnic minority,” Haley told the U.N. Security Council.

The United States had earlier said the army response to the insurgent attacks was “disproportionate” and the crisis raised questions about Myanmar’s transition to democracy, under the leadership of Nobel laureate Aung San Suu Kyi, after decades of military rule.

China and Russia, however, both expressed support for the Myanmar government. Myanmar said this month it was negotiating with China and Russia, which have veto powers in the Security Council, to protect it from any possible action by the council.

Suu Kyi has no power over the generals under a military-drafted constitution that bars her from the presidency. She has nevertheless drawn scathing criticism from around the world for failing to speak out more strongly and stop the violence.

Rohingya Muslim women stretch their arms out to collect sanitary products distributed by aid agencies. Dar Yasin / AP

The military campaign against the Rohingya insurgents is well supported inside Myanmar, where Buddhist nationalism has surged over the past few years.

Haley said the military must respect human rights and fundamental freedoms.

“Those who have been accused of committing abuses should be removed from command responsibilities immediately and prosecuted for wrongdoing,” she said.

“And any country that is currently providing weapons to the Burmese military should suspend these activities until sufficient accountability measures are in place,” Haley said.

Myanmar national security adviser Thaung Tun said at the United Nations there was no ethnic cleansing or genocide in Myanmar.

He told the Security Council that Myanmar had invited Guterres to visit. A U.N. official said the secretary-general would consider visiting under the right conditions.