By Jonathan Head
BBC News, Bangkok
Thai authorities insist the Hmong in Thailand are economic migrants
Aid agency Medecins Sans Frontieres says it is pulling out of a relief effort in Thailand for about 5,000 ethnic Hmong asylum seekers from Laos.
The organisation cited pressure and intimidation by the Thai military.
Some members of the Hmong have been involved in an armed insurgency against the communist government in Laos since the end of the Vietnam war in 1975.
Hundreds have been forcibly returned by the Thai authorities, and face almost certain persecution, MSF says.
MSF says this was a difficult decision to make.
It is the sole international organisation allowed to work in the camp in northern Thailand which still houses nearly 5,000 ethnic Hmong who fled from Laos four years ago.
It provides most of the food and medical treatment for them.
But, says Gilles Isard, who heads the MSF mission in Thailand, the increasing restrictions imposed by the Thai military on its activities and the army's harassment of the Hmong have forced it to pull out.
"More and more, the Thai army is trying to use coercive measure to force the people to return to Laos. Also they are pressuring MSF.
"For instance they have been trying to demand MSF stop providing food distribution to the people in order to punish them," he told the BBC.
The Hmong have been engaged in an intermittent insurgency against the communist government in Laos ever since the Vietnam war when many of them were recruited into a secret CIA-run army to combat the advancing communist forces.
Some of those in the Thai camp have bullet wounds and most, say MSF staff, are terrified at the prospect of being sent back.
Yet that is what the Thai government insists it will do despite protests by the UN refugee agency and others.
Foreign Minister Kasit Piromya insists no international monitoring is necessary.
"If there is a problem we need to review our own process first and the international people could be in the advisory capacity that could be done," he said.
If the Hmong are being held in overcrowded jails by the Thai military, journalists and most international organisations are barred from entering the camp.
The Thai government says it alone will ensure those Hmong who are repatriated are well treated, but in a secretive authoritarian state like Laos it is not clear how it can do that.