BANGKOK (AFP) - A leading rights group Saturday called on the Thai government to allow 158 Lao Hmong refugees, who have been detained for three years pending deportation, to be resettled in four western countries.

New York-based Human Rights Watch said the group were being "held in poor and abusive conditions" and should be allowed to leave for the United States, Canada, the Netherlands, and Australia, which have agreed to resettle them.

"Thai authorities have kept Lao Hmong refugees in fear and uncertainty for years to pressure them into giving up hope of refuge in Thailand or resettlement elsewhere," said Brad Adams, the group's Asia director.

"The government should immediately end this immoral and unlawful policy," he said in a statement.

Human Rights Watch in the statement said it had sent a letter to Thai Prime Minister Abhisit Vejjajiva that also raised concerns about the ongoing detention of some 5,000 Hmong being held in Phetchabun in northeast Thailand.

The immigrants are expecting to be deported to Laos following an agreement between the countries.

Tens of thousands of ethnic minority Hmong have sought asylum in Thailand, claiming that they face persecution from the communist Laos regime as they had fought alongside US forces during the Vietnam war.

Large numbers have since been resettled in western countries, including the United States.