By Jonathan Head
BBC News, Bangkok
Hmong women cry after being told they will be sent back to Laos
For the past four years, thousands of ethnic Hmong, who have fled from their homes in the mountains of northern Laos, have been living a precarious existence in the Thai province of Phetchabun.
After initially trying to survive in the forest, they were moved by the Thai military into a camp, to which access is strictly controlled.
Almost all outside agencies are banned from entry.
Repeated requests by the UN refugee agency to be allowed to screen them and assess their claims that they face persecution or death if sent back to Laos have been refused by the Thai authorities.
Every now and again groups have been forcibly repatriated to Laos; the rest remain trapped, living in constant fear.
One group of 158, which includes many children, has been held for two and a half years in a cramped detention centre in the border town of Nong Khai. Others are being held in jail.
The only international organisation allowed to help the almost 5,000 Hmong in Phetchabun has been Medecins Sans Frontieres (MSF), which has been their sole source of food and healthcare. Now MSF has decided to pull out, citing unacceptable pressure from the Thai military.
"We can no longer work in a camp where the military use arbitrary imprisonment of influential leaders to pressure refugees into a 'voluntary' return to Laos," said Gilles Isard, head of the MSF mission in Thailand.
"Also there are pressures on MSF. For instance they have been trying to get MSF to stop food distribution to the people in order to punish them."
MSF staff describe the Hmong as living under extreme psychological stress, because of the constant threat of repatriation. Some have threatened to kill themselves, rather than return. Many carry bullet wounds; they say they fear retribution by the Lao communist authorities if they go back.
MSF has been running a health clinic just outside the camp, but says the Hmong stopped coming after they were forced to report to a Thai military checkpoint first.
The checkpoints are where the Thai authorities sometimes whisk Hmong away for deportation.
More than 1,500 have already been forced back over the border. Their fate is still uncertain, as the Lao government refuses to allow international agencies to monitor the returnees.
According to Amnesty International, 20 women and girls sent back to Laos in December 2005 were detained for 18 months, and some were tortured.
Other returnees have vanished.
The Hmong are a large hill tribe, who inhabit mountainous areas of south-east Asia.
During the Vietnam War, many of them were recruited into a secret army run by the CIA, to help fight against the advancing communist Pathet Lao forces. When the Americans pulled out, the Hmong found themselves on the losing side.
Joua Va Yang holds a photo of Ruhi Hamid, who made the BBC film
They were subjected to harsh treatment by the new communist government. Some started a desperate armed campaign against the government, which they have kept up intermittently until now. Lao forces have responded in kind, at times bombarding Hmong areas from the ground and air.
Among the Hmong leaders is Joua Va Yang, who in 2004 helped guide a BBC team into a rebel area to make the first TV documentary about the plight of the Hmong who were trapped there.
He is now being held in jail in Phetchabun, after being arrested at the camp.
The Thai military say he has volunteered to go back to Laos, despite an obvious risk of retribution over his role in the documentary. No-one has been allowed to see him to hear his own views.
So why is Thailand taking such a hard line against the fleeing Hmong? Many would be eligible for resettlement in the United States, if only they could be screened by agencies like the UNHCR.
There is no easy answer. Over the years Thailand has had to host millions of displaced people from conflicts in neighbouring countries. Some have been allowed to stay. Others have been kept in camps, like the Hmong, where access to international agencies is tightly restricted.
Little information has come out from those already sent back to Laos
The army, a very powerful player in Thai politics, routinely demands a big say over how they are treated.
Earlier this year military units were accused of towing asylum-seekers from Burma's Rohingya minority out to sea, and casting them adrift with little food and water.
The military appears to view some groups as a security threat, or as an unwanted complication in their ties with neighbouring armies.
But the fate of the Hmong seems sealed.
The Thai Foreign Minister, Kasit Piromya, told the BBC that he had already agreed with his Lao counterparts to send them back soon.
On a recent trip to Washington DC, the famously loose-tongued Mr Kasit said one Hmong group would be allowed to go to the US - only to back-track after the Lao government protested.
When asked why no international screening or monitoring of the Hmong was being allowed by Thailand, Mr Kasit would only say that such screening was unnecessary, and that he was prepared to trust the assurances of the Lao government.
Medecins Sans Frontieres, the UNHCR and many other agencies strongly disagree.