United Nations Secretary-General Ban Ki-moon said on Thursday that he is alarmed by reports that some countries in Southeast Asia may be refusing entry to boats adrift at sea with several thousand refugees and migrants.
Thailand declined permission for a migrant boat to land on Thursday while Malaysia said it would push boats back out to sea.
"The secretary-general urges governments to ensure that the obligation of rescue at sea is upheld and the prohibition on refoulement is maintained," UN spokesman Stephane Dujarric told reporters.
"He also urges governments to facilitate timely disembarkation and keep their borders and ports open in order to help the vulnerable people who are in need," he said.
Smugglers have abandoned ships full of migrants, many of them hungry and sick, following a crackdown on human trafficking in Thailand, the most common first destination for Rohingya Muslims fleeing persecution in Bangladesh and Myanmar.
An estimated 25,000 Bangladeshis and Rohingya boarded rickety smugglers' boats in the first three months of this year, twice as many in the same period of 2014, the UN refugee agency UNHCR has said.
The UNHCR estimates that around 300 people died at sea in the first quarter of this year as a result of starvation, dehydration and abuse by boat crews.
Ban "emphasizes the need for a timely, comprehensive, rights-based, predictable and effective response" to the crisis, Dujarric said.