The United Nations High Commissioner for Refugees (UNHRC), António Guterres, appealed on Thursday to the Thai government, saying the proceeding would endanger the protection and set grave example.
"In accordance with international law, Thailand has the responsibility and international obligation to ensure that any return of recognized refugees or other persons in needs of international protection to their country of origin is undertaken on a strictly voluntary basis," he said.
"To proceed otherwise would not only endanger the protection of the refugees but set a very grave international example."
Meanwhile the US Department said Thursday that it was deeply concerned about the fate of the Hmong, an ethnic minority that some of them battled the communist movement of Pathet Lao for years with U.S. support before the fall of Vientiane in 1975.
New York-based Human Right Watch sent a letter to Prime Minister Abhisit Vejjajiva Thursday to prevent the massive deportation of the Hmong.
Thailand has long maintained that the Lao Hmong asylum seekers in Huay Nam Khao camp are illegal migrants who may be deported to Laos.
"But under customary international law the Thai government has an obligation not to forcibly return persons to places where their life or freedom is at risk (nonrefoulement)," the letter said.
Human Rights Watch is concerned that international standards have not been met regarding screening measures to determine whether the individuals in Huay Nam Khao have legitimate protection concerns should they be returned to Laos, it noted.
Thai military from the Third Army Region was moving some 50-70 trucks and buses to transport the Hmong from Ban Huay Nam Kho in Phetchabun's Khao Koh district. A military officer who oversees the camp said the authority would remove them from the camp in a week before the end of this year.
The Hmong claimed they are close associates of the US Central Intelligence Agency (CIA)'s secret fighters against Communist Phathet Lao during Vietnam War but left over since 1975. They fled from suppression at home.
However, Thailand and Laos regarded them as normal economic migrant who sought better lives, not asylum seekers.
In fact, the are some 47 families who really have connection with the CIA secret war and international community questioned Thai military screening process as it was conducted without transparency and participation of international community notably the UNHCR.
Another group of 158 Hmong was being detained in Nong Khai detention center pending the repatriation although many of them obtained UN protection as person of concern since 2006.