Thai soldiers are detaining illegal migrants from Bangladesh and Burma and forcing them back out to sea in boats without engines, survivors say.
Survivors say their hands were tied and they were towed out to sea with little or no food or water.
About 500 migrants are now recovering from acute dehydration in India's Andaman islands and the Indonesian province of Aceh. Thai officials were not immediately available for comment.
But sources in the police and army confirmed to the BBC's Jonathan Head in Bangkok that asylum seekers are being pushed out to sea. They did not provide further details about the practice.
Thousands of poor Burmese and Bangladeshis try to reach south-east Asian nations in search of work.