HANOI (AFP) -- Thousands of Lao Hmong are stuck in limbo in Thai camps as Bangkok and Vientiane discuss their fate in a case mixing the Vietnam War legacy with the quest of poor villagers for a better life abroad.

Around 6,500 people from the ethnic minority group live in Phetchabun camp in northeastern Thailand, where they are awaiting a diplomatic solution between the neighbors and the possible intervention of a third party to help them.

Until mid-2006, the communist rulers of isolated Laos refused to address the issue, which they dismissed as "a Thai internal affair".

But more recently, Vientiane has said it is willing to take back those Hmong who can prove they are Lao citizens and not from another country, as long as no third party is involved in the repatriation process.

The issue is far from resolved. Politically, it is highly sensitive.

Some Hmong, a hilltribe people, were allied with the United States during the "Secret War" in Laos that was part of the wider Vietnam conflict.

After the war ended in 1975, according to various estimates, around 150,000 Hmong fled persecution by the victorious communist regime, finding new homes mostly in the United States and 26 other countries.

Hmong made up about half of all the Lao nationals who fled the country, experts say.

Others hid in the dense Laotian jungle where a handful of fighters have until recently fought a low-level insurgency which, their supporters say, has been met with brutal repression from Lao forces.

Fuelling the exodus since then have been villagers hoping to escape rural poverty in Laos, one of Asia's poorest nations.

"The migrations in Thailand are part of the chain migrations that have happened since 1975," said Grant Evans, a Laos expert at Hong Kong University. "In the early days after the war, people escaped because they were scared. Now, many see it as an opportunity to join families in the United States."

But the U.S. resettlement program ended in 2003, and Washington is now keen to avoid a "magnet effect" of more Hmong fleeing to Thailand in the mistaken belief they will be allowed to live in America.

Today, the international community is urging Bangkok to classify the Hmong people on its territory as political refugees and economic migrants.

Kitty McKinsey, Asia-Pacific spokeswoman for the UN High Commissioner for Refugees (UNHCR), said the Hmong in Phetchabun should be screened to find out how many of them have indeed fled persecution. "We are not insisting that UNHCR has to do it," she said. "We would be happy to help the Thais if they asked for help. It could be done by the Thai government as long as it is done to international standards."

She said many in the camp were probably economic migrants, but that if some people were genuinely "in fear of persecution, in fear for their lives, in fear that their human rights would be violated," then they must be protected.

Vientiane has never accepted the existence of the Hmong rebels, who have troubled security in northern Laos and have been blamed for bloody ambushes on tourist buses which killed dozens of people in 2003.

The families of many Hmong have surrendered in the past two years, and analysts say there are so few fighters left that the problem is about to end.

But Vientiane keeps denying a problem ever existed. Lao officials "are caught up in their own dogmatism," said a foreign expert, who asked not to be named. "They've always denied the Hmong rebels exist. Now they would have to backtrack and reconstruct history, and they don't want to."

The silence only grew heavier after some 26 Hmong children were illegally repatriated from Thailand in December 2005.

No-one has heard from them since.

"If there is no persecution, if there is no threat to life, then why doesn't the government of Laos let independent monitors go in and see what happened to the children?" asked McKinsey.

In a more recent case, 152 Hmong were arrested in Thailand in November.

McKinsey said the UNHCR would be "extremely alarmed" if they were sent back to Laos, as they have all either been granted refugee status or have their applications pending.

But Laos said last week they were currently preparing to take them back after Amnesty International said "Lao officials have been allowed to interview and photograph members of the group" in Thailand.

Vientiane denied they were refugees.

"There is no war, there is no conflict, there is no violence, there is no genocide," Foreign Ministry spokesman Yong Chantalangsy said.

Sunai Phasuk, Thailand representative for New York-based Human Rights Watch, said Thailand's new military-installed leaders will end up violating a widely recognized international principle if they deport the 152 Hmong refugees.

On the 6,500 Hmong in Phetchabun, he said he recognized Thailand was taking a hard line to discourage human traffickers, but urged Bangkok not to do this at the expense of genuine refugees.

Thailand, he said, should allow the UNHCR to have access to the Hmong and convince Laos to allow monitoring on its territory too. "This is the job of a good diplomat," he said, "to try to persuade the other side to respect the international standards."