BANGKOK, Thailand (CNN) -- Thailand's military has denied abusing refugee boat-people from Myanmar after claims some were whipped on a tourist beach and hundreds more left dead or missing after being towed at to sea without food and water.
Photograph released by Thai navy showing a group of illegal immigrants captured on December 12.
Photos showing refugees being made to lie face down on a popular beach and media reports claiming refugees been deliberately lost at sea have sparked concerns for their safety.
The United Nations High Commissioner for Refugees says it is "concerned" about the fate of the Muslim ethnic minority Rohingya people, who have fled from Myanmar's border with Bangladesh.
The agency says it has written a formal note to the Thai Ministry of Foreign Affairs asking for clarification of what is happening.
CNN spoke to one Australian tourist, who declined to be named for fear of being barred from Thailand, who says boat-people were "whipped" by Thai guards on popular diving resort island in the Similan Archipelago last month.
Local media also report claims by Rohingya survivors that the Thai military have been detaining hundreds of them an island called Koh Sai Daeng before towing them back out into open water without supplies.
The survivors say hundreds of them drowned and only the lucky ones made it to the Indian Andaman Islands or Indonesia's Aceh province.
The Thai Navy denies knowledge of the incident.
Rear Admiral Naris Pratumsuwan told CNN "as a normal practice, if Navy finds illegal immigrants, we will hand them over to related authorities, e.g. police or immigration police."
He said he had not received any information on an island where migrants are being detained.
There were reports of another boatload of 46 Rohingya detained by the Thai military Friday, but there was no official confirmation.
The Rohingya have been fleeing persecution of the hard-line military regime in Myanmar, formerly Burma, for years and often seek refuge in Malaysia.
Boat loads of Rohingya arriving in Thailand is nothing new, but non-governmental organizations are increasingly worried about what they say is an apparent change of government policy.
They say the army's Internal Security Operations Command is forcing the Rohingya out to sea rather than deporting them overland back to Myanmar.
"The Thai government is taking highly vulnerable people and risking their lives for political gain," says Refugee International's Sean Garcia says.
"It should be engaging the Burmese government on improving conditions at home for the Rohingya if it wants to stem these flows.
"The Rohingya will continue to make the journey because they have no hope for a better life in Burma. Pushing them back out to sea is not an effective deterrent it just jeopardizes lives."