Around 300 men, women and children were found pleading for help Thursday on the drifting trawler which has become emblematic of Southeast Asia's growing migrant crisis and the region's reluctance to offer sanctuary to the passengers.
The Thai navy said it had repaired the engine and provided visibly thin passengers with food, water and medicine on both Thursday and Saturday before "escorting" the vessel into international waters.
Thai authorities insist the passengers wanted to travel southwards onto Malaysia and say they have had no news of the vessel since around 9 pm Saturday.
"We don't have any information on that boat," Thai navy official Veerapong Nakprasit told AFP this morning.
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Indonesian and Malaysian officials have declined to comment on the status of a vessel which has been subject to what one rights group has coined "maritime ping-pong".
Chris Lewa of The Arakan Project, a Rohingya rights group that monitors boat crossings, said her team were last in contact with the ship by telephone on Saturday evening.
"It's very worrying," she told AFP.
"They had told us that the men were taking all the food and that the women could not get the food. They were only getting little bits left over. That was the last we heard from them."
Survivors from another vessel that washed up in Indonesia on Friday said at least 100 people had died in fighting between Bangladeshi and Rohingya migrants over meagre rations.
"These boat people have been at sea for weeks and months, without adequate food or any sort of medical care, and they are in a greatly weakened state," said Phil Robertson, deputy Asia director for Human Rights Watch.
Nearly 3,000 Myanmar Rohingya and Bangladeshi migrants have swum to the shore or been rescued off Indonesia, Malaysia and Thailand over the past week while others have been turned back to sea in moves triggering international outrage.
Tens of thousands of Rohingya, a persecuted Muslim minority in Myanmar, have fled the country in barely sea- worthy boats across the Bay of Bengal.