The UN migration agency says more than 60 people are either confirmed dead, or missing and presumed dead following the shipwreck of a boat carrying Rohingya Muslims who were fleeing from violence in Myanmar to Bangladesh.
Spokesman Joel Millman of the International Organisation for Migration told reporters in Geneva that 23 deaths have been confirmed.
The refugees drowned in heavy seas off Bangladesh late on Thursday while, in New York, US Ambassador to the United Nations Nikki Haley called on countries to suspend provisions of weapons to Myanmar because of violence against Rohingya muslims.
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.
More than 500,000 Rohingya have fled to Bangladesh since then.
Based on interviews that IOM has conducted with survivors, Millman said, "We believe 40 are missing and presumed drowned" on the vessel, which was thought to have been carrying about 80 people.
The "very tragic" accident involved a vessel that had been at sea for two days with no food and had faced choppy seas, Millman said. The Bangladeshi captain had not initially charged the passengers any fee for the transport and had been trying to avoid sea patrols or checkpoints, he said.
"The details are absolutely astonishing and remarkable," Millman said. "At one point, he (the captain) chose to anchor the vessel, but that proved to be a fatal mistake as the rough seas were much worse than he supposed. This was easily within sight of land."
United Nations Secretary-General Antonio Guterres told the Security Council the violence has spiralled into the "world's fastest developing refugee emergency, a humanitarian and human rights nightmare".
