More than 50 Rohingya refugees from Myanmar are missing after their boat capsized, with 19 confirmed dead, Bangladesh police said on Friday, as a new surge in the numbers fleeing a Myanmar military campaign took the total to more than half a million.

The refugees drowned in heavy seas off Bangladesh late on Thursday while, in New York, US Ambassador to the UN Nikki Haley called on countries to suspend providing weapons to Myanmar over violence against Rohingya Muslims.

It was the first time the US had called for punishment of Myanmar’s military leaders behind the repression, but she stopped short of threatening to reimpose US 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 sweeping military offensive in response to coordinated attacks on the security forces by Rohingya insurgents in the north of Rakhine State on August 25.

Refugees arriving in Myanmar have told of attacks and arson by the military and Buddhist vigilantes aimed at driving Rohingya out.

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

Bangladeshi border officials said more refugees had arrived over the past day or two after the number seemed to be tailing off. Aid groups said 502,000 refugees had arrived in Bangladesh since late August.

“It stopped for a while but they have started coming again,” Colonel Anisul Haque, head of the Bangladeshi border guards in the town of Teknaf, told Reuters.

“Last night, we got a number arriving. They seem to think it will be difficult to cross during the day because security forces will make it difficult for them,” he said.

He said about 1,000 people had landed at the main arrival point on the coast on Thursday.

The boat carrying refugees went down in driving wind and rain and high seas. The International Organisation for Migration said about 130 people were believed to have been on board.

Bangladesh police said there were 27 survivors, 19 dead and more than 50 missing.

‘Brutal campaign’

In a sharp ramping up of the pressure on Myanmar, also known as Burma, Haley echoed UN 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 UN Security Council.

The US 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.

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.

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, 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 UN there was no ethnic cleansing or genocide in Myanmar.

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

China and Russia 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.