BANGKOK: The United Nations called for access to thousands of ethnic Hmong deported to communist Laos from neighbouring Thailand as Bangkok insisted Wednesday that the returned people would be treated well.

Thailand on Monday completed the repatriation of more than 4,000 Hmong, including children, sending in troops to clear them from camps on the border despite international calls to halt the operation.

The Hmong, a Southeast Asian ethnic group, were seeking asylum in Thailand saying they risked persecution by the Laotian regime for fighting alongside US forces in the Vietnam War during the 1960s and 1970s.

UN chief Ban Ki-moon voiced regret late Tuesday over Thailand's expulsion of the Hmong and urged the two countries to take steps to protect the rights of the deportees.

Ban "regrets that these deportations have taken place in the face of appeals from the United Nations High Commissioner for Refugees (UNHCR) and despite the availability of third country resettlement solutions for those recognised as refugees," said a statement released by his press office.

In Geneva, the UNHCR said it had filed a formal request with Laos for access to the Hmong and urged Thailand to provide details on a Thai-Laotian accord that governed how Hmong returnees should be treated.

"UNHCR has asked to be informed of steps taken by the Government of Thailand to ensure that commitments made under this framework are effectively honoured," it said.

Thailand on Monday also sent back a separate group of 158 Hmong with recognised UN refugee status, in a move the UNHCR said was a breach of international law.

In Bangkok, Thai foreign minister Kasit Piromya Wednesday tried to quell international concerns.

"Laos has promised Thailand that they will give good treatment to these people. They will not be jailed and they will be given passports and a chance to meet with third countries that could resettle them," Kasit told reporters.

"We are confident that they will proceed as promised."

Kasit said that the international community should also "help develop Laos to strengthen Laos" if they wanted to ensure the good treatment of the Hmong.

Both Thailand and Laos say that the Hmong were illegal immigrants and not political refugees as they contended, but the deportation has drawn fierce international condemnation.

US lawmakers on Tuesday denounced Bangkok and demanded that the Vientiane government allow immediate international monitoring to ensure their safety.

The senators representing Minnesota and Wisconsin, states home to much of the Hmong community in the United States, said they "strongly condemn" Thailand.

"This action violates humanitarian and refugee principles and could have serious repercussions," said the statement by Senators Russ Feingold and Herb Kohl of Wisconsin and Al Franken and Amy Klobuchar of Minnesota.

Rights group Amnesty International also said there were concerns that provisions to meet the humanitarian needs of the returnees in Laos were inadequate.

Thousands of Hmong, a highland people, sided with the United States during the Vietnam War and formed a CIA-funded "secret army" when the conflict spread to Laos.

When the Communists took power in Laos in 1975, Hmong fighters feared the regime would hunt them down for working with the Americans. About 150,000 fled and found homes abroad, mainly in the United States.

Others hid in the Lao jungle, some fighting a low-level rebellion that has been largely quashed. Thousands have fled to neighbouring Thailand, which also backed the United States in the war.