A United Nations human rights investigator on Myanmar voiced deep concern on Monday at Bangladesh's plan to relocate 23,000 Rohingya refugees to a remote island in April, saying that it may not be habitable, creating a potential "new crisis".

Bangladesh says moving refugees to Bhasan Char - whose name means "floating island" - will ease chronic overcrowding in its camps at Cox's Bazar, which hold some 730,000 Rohingya. The U.N. says the Muslim minority fled mass killings and rapes committed during an army crackdown in western Rakhine state since August 2017.

Some humanitarian groups have criticized the relocation plan, saying the island is vulnerable to frequent cyclones and cannot provide a livelihood for thousands of people.

"There are a number of things that remain unknown to me even following my visit, chief among them being whether the island is truly habitable," said Yanghee Lee, U.N. special rapporteur on Myanmar, who visited the island in the Bay of Bengal in January.

"Ill-planned relocation, and relocations without the consent of the refugees concerned, have the potential to create a new crisis. It is incumbent on the government of Bangladesh to ensure that this is not brought about," she told the U.N. Human Rights Council.

There was no immediate reaction from the Dhaka government.

Lee, who is banned by Myanmar's government from visiting, also told the Geneva forum that up to 10,000 civilians are reported to have fled their homes in Myanmar's Rakhine state since November due to violence and a lack of humanitarian aid.

She urged the U.N. Security Council to refer alleged atrocities against Rohingya and other ethnic groups in Myanmar to the International Criminal Court (ICC) and encouraged Yangon to accept its jurisdiction.

But Myanmar's ambassador, Kyaw Moe Tun, promptly rejected this, saying The Hague-based court had "no jurisdiction over Myanmar whatsoever".

"Whilst the government is unable to accept this legally dubious intervention by the ICC, Myanmar is fully committed to ensuring accountability where there is credible evidence of human rights violations committed in Rakhine State," he said.

The most pressing task is to focus on a speedy start to repatriating the refugees, he said, without using the word 'Rohingya' - who are mostly stateless in Myanmar.