Bangkok - At least 3,000 Burmese refugees must abandon their lives in Bangkok and go to overcrowded border camps to avoid deportation under a new deadline imposed by the Thai government.

The refugees from Burma's military regime, who have been granted "person of concern" status by the United Nations high commissioner for refugees (UNHCR), have been given a deadline of March 31.

"If you do not register for transfer to the camp, you will not be resettled to a third country ... you will no longer receive assistance in any form," it has warned the refugees in a letter.

"You will be regarded as an illegal migrant without permission to remain in Thailand. As such, you may be subject to arrest, detention and deportation," it adds.

The refugees are told they could not take furniture, pets, electrical appliances or mobile phones to the camps.

"You will not have an opportunity to return to your homes after registration and will not be allowed to go freely in and out of the camp," the letter says.

UN officials say they are concerned about the little time available for refugees to cancel house rental agreements, sell possessions and prepare for life in crowded camps. A detention centre in Bangkok is ready to receive them.

Only about 30 refugees had moved from the city to one of the camps by yesterday and another 40 had registered to move. NGOs involved in caring for the refugees have requested an extension of the deadline, but there is little hope of it being granted.

About 140,000 Burmese have lived in border camps for many years and are undergoing registration by the UNHCR. Three camps have been chosen to receive the 3,000 urban refugees: Nu Po camp in Tak province, Ban Don Yang camp in Kanchanaburi province, and Tham Hin camp in Ratchaburi province.

"Currently there is housing available for up to 500 people, while additional housing is being constructed. There is not sufficient space for 3,000 people at the moment. We are working with the government to find out where more structures can be built," Bernard Quah, assistant regional representative for the UNHCR operations, told the Guardian.

NGO sources said the camps were isolated and food supplies had to be brought in and stockpiled. But with the rainy season under way, transport, construction and other practical tasks were more difficult.

Refugees already in the camps live in bamboo shelters, some of them in long-houses holding up to 60 people. There is little for them to do all day, no jobs and no guarantee of resettlement abroad.

Refugees have been fleeing Burma for decades to escape the military dictatorship, brutal repression and economic stagnation. The flow increased with the crushing of the democracy movement led by Aung San Suy Kyi in the late 1980s. Regular crackdowns on dissent prompt new flows to the border.

The Thai government's primary goal is to prevent Thailand becoming a desirable destination for refugees.