By Tommy Wilkes and Michelle Nichols

COX'S BAZAR, Bangladesh/UNITED NATIONS, Sept 29 (Reuters) - M ore 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, U.S. Ambassador to the United Nations Nikki Haley called on countries to suspend providing weapons to Myanmar over violence against Rohingya Muslims.

It was the first time the United States had called for punishment of Myanmar's military leaders behind the repression, 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 sweeping military offensive in response to coordinated attacks on the security forces by Rohingya insurgents in the north of Rakhine State on Aug. 25.

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

United Nations 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 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.