Bangkok  - The Thai military blocked food supplies over the weekend to a Hmong refugee camp in an apparent effort to force the 5,400 "illegal immigrants" to return to Laos, media reports and aid agencies said Monday.

On Friday the military prevented Medicins Sans Frontieres (Doctors Without Borders) from delivering food supplies to Ban Huay Nam Khao camp in Phetchabun province, 250 kilometres north-east of Bangkok.

"We couldn't go in on Friday but on Monday we were allowed back in," Medicins Sans Frontieres Thailand representative Gilles Isard said.

Hmong leader Lee Sue has called on Thailand's National Human Rights Commission to investigate the military's conduct, The Nation newspaper reported.

The Thai military reportedly cut off the food supplies to punish the Hmong camp inmates for refusing to be counted, seen by some Hmong as a first step towards forced repatriation to Laos.

The Hmong are an ethnic minority group from neighbouring Laos who provided the main guerrilla force for the US military in its "Secret War" against the spread of communism in the land-locked country in the 1960s and 70s.

After Laos went communist in 1975, hundreds of thousands of Hmong fled Laos and were resettled in the US. Thousands more have stayed in Thailand, but they are under increasing pressure to join repatriation programmes.

Ban Huay Nam Khao, supervised by the Thai military, has provided a home for Hmong refugees since 2004. Last month the camp invited Lao officials to Ban Huay Nam Khao to persuade the residents to return to Laos.

Camp residents claim the Thai authorities have been using new tactics to persuade the Hmong to return, such as making frequent arrests of camp inmates for minor offences such as gambling.

Since November, about 200 Hmong have voluntarily returned to Laos from the camp each month, aid workers said. Thailand identifies the camp residents as "illegal migrants," refusing to acknowledge them as refugees despite their claims of political persecution in Laos. (dpa)