Campaigners have been stepping up pressure on Thai authorities in recent days, warning the group of 1,700 refugees, mostly women and children, would face possible rape, torture or execution at the hands of Myanmar soldiers, or could be killed by numerous landmines laid around their villages.
The group of refugees had fled to Thailand following an upsurge in a Myanmar government offensive against Karen fighters.
"They will undoubtedly be subject to forced labour, executions, torture and mutilations, forced recruitment as soldiers, including child soldiers, and theft and extortion, making their survival very difficult"
Letter from 27 US legislators to Thai PM
Earlier this week US lawmakers and a coalition of human rights groups urged the Thai government not to go ahead with what they said was a forced repatriation.
Zoya Phan, of the Burma Campaign UK, one of the groups campaigning for the refugees, told The Independent newspaper that any moves to force their return would be "sending them back to possible death, slave labour or forced recruitment as soldiers".
"If refugees are now forced to return it will not only be morally unacceptable, it will also damage the reputation of Thailand in the eyes of the world."
Thai officials however have denied that anyone would be forced to leave, saying any repatriations would be on a voluntary basis.
"There is no forced repatriation as it's not our policy," Colonel Noppadol Watcharajitbaworn, military commander in the Thai province of Tak where the refugees are sheltering, told the Associated Press.
He said a first batch of more than 100 people had volunteered to return to their village on Friday.
|Campaigners say refugees told them they had been threatened by Thai soldiers [EPA]
"We will not force them back if they don't volunteer to go," Noppadol said, adding that the area around their village was safe and landmines were not a problem.
His comments followed claims from the Karen Human Rights Group that Thai soldiers had been visiting the Karen refugees, some up to three times a day, to pressure them with threats that they must leave by February 15.
Citing interviews with refugees the group said Thai soldiers told the refugees they would be forced to leave if they do not go voluntarily.
"If you do not go back, we will ask big trucks to come pick you up and throw you all into the sea," one refugee quoted a soldier saying.
Benedict Rogers, a spokesman for Christian Solidarity Worldwide, said the situation was an urgent one requiring immediate international attention, and called on Thailand to continue to provide the refugees with shelter and protection.
"There is a severe risk that if they return, the Karen refugees will be subjected to severe human rights violations, including forced labour and rape" by Myanmar government troops.
On Thursday a group of 27 US legislators echoing similar concerns appealed to Thailand against sending the refugees back to Myanmar.
"If forced to return, these refugees will suffer horrific human rights abuses," said the letter to Abhisit Vejjajjiva, the Thai prime minister.
"They will undoubtedly be subject to forced labour, executions, torture and mutilations, forced recruitment as soldiers, including child soldiers, and theft and extortion, making their survival very difficult."
There are about 160,000 long-term refugees in camps along Thailand's border with Myanmar, many of them having fled fighting between government soldiers and ethnic rebel groups.