Five hundred men are now missing feared drowned.

Survivors who were rescued by Indian coastguard 12 days after they were set adrift have told harrowing accounts of their treatment by the Thais.

They said that with their hands tied they were forced at gunpoint onto a barge. "[They] ordered us to get on that boat. We all denied. First they pointed their guns at us, but we still refused to move. Our hands were already tied on the navy ship but this time they also tied the legs of some people and threw four of them into the sea," one survivor, Mohamed, recounted in a telephone interview.

"Once we were all on it, they untied our hands. Afterwards, they continued to tow us for some time and then all of a sudden they cut the towing rope and left."

That was the first of two refugee pushback operations mounted by Thailand in the past month. On or about December 18, more than 400 men, mainly of Muslim Rohingya ethnicity, from Arakan state in Burma, were set adrift. Rescuers found 107; 300 jumped into a strong current on seeing a lighthouse in the distance but only a handful made it to shore.

Thailand faces the possibility of bodies washing up on beaches in Phang Nga and Phuket at the height of the tourist season.

The Foreign Minister, Kasit Piromya, has proposed a meeting with ambassadors from Burma, Malaysia, Bangladesh, Indonesia and India. The Prime Minister, Abhisit Vejjajiva, met human rights activists and announced an investigation into the allegations.

A spokesman for Australia's Department of Foreign Affairs said yesterday: "The Government has been concerned to read of allegations of the mistreatment by Thai security forces of Rohingya people arriving in Thailand by boat over recent weeks. The Australian embassy in Bangkok has been following up this matter with relevant Thai agencies, as well as UNHCR."

In a second pushback, about December 30, four boats without engines carrying 590 refugees were set adrift in open water. One carrying 193 washed up in Aceh, a second carrying 150 drifted to the uninhabited Tillanchang Island. Two boats with 237 on board are reportedly missing.

The harsh policy was introduced by the Thai army's Internal Security Operations Command in December when it took control of refugee matters from civilian immigration services, the South China Morning Post reported.

It has published photographs of Colonel Manat Khongpan, a regional commander in ISOC, supervising tens of handbound refugees on Sai Daeng beach. Contacted by the Herald yesterday, Colonel Manat denied involvement. "I don't do that. I don't have anyone. My work is not doing about refugees."

Since 2006 the number of refugees has doubled each year from 1200 to 5000 last year. It is understood that ISOC has become concerned at the number of young Muslim men sailing from Burma, where they are stateless and severely persecuted, through Thailand to Malaysia.

Thailand is fighting a Muslim insurgency in its southern provinces, which border Malaysia. But Chris Lewa, director of the Arakan Project that researches the plight of the Rohingya, rejected any notion that they were linked to the insurgency, saying she had seen no evidence of it.