At least 2,000 desperate migrants, including women and children, are at risk of violence and food shortages after more than 40 days trapped on boats off Myanmar, the UN refugee agency said Tuesday.
The group have been "stranded on at least five boats near the Myanmar-Bangladesh coasts for more than 40 days", United Nations High Commissioner for Refugees spokesperson Vivian Tan told AFP, adding that unconfirmed reports put the number even higher.
It was unclear if the people-smugglers who had organised the voyage were still on board the boats.
A recent Thai crackdown on people-smuggling has blocked the southwards route through that country to Malaysia, disrupting the traffic.
As a result nearly 3,000 Rohingya and Bangladeshi migrants have arrived off Indonesia, Thailand and Malaysia in recent days. Thousands of others are feared trapped at sea after being abandoned by people-smugglers.
Tan said some migrants on the five boats had paid smugglers around $300 each to return to Myanmar's Rakhine state, where hundreds of thousands of Rohingya Muslims live in abject poverty and suffer discrimination.
Those who have returned to land have said passengers still on the boats are short of food and water, while reports of violence are "causing great concern", Tan added.
Myanmar's government on Monday acknowledged international concerns about waves of boatpeople, many of them Rohingya fleeing Rakhine, but has urged a joint regional response to the crisis.
Information minister Ye Htut said Myanmar's navy had begun preparing to search for vessels in the country's waters, but anyone returning would have to prove their nationality.
Myanmar does not recognise the estimated 1.3 million Rohingya as an official minority, instead viewing them as mostly illegal immigrants from Bangladesh.