Thai troops packed more than 4,000 ethnic Hmong into military trucks Monday for a one-way journey to Laos, all but ending the Hmong's three-decade search for asylum following their alliance with the U.S. during the Vietnam War.

The United States and rights groups have said the Hmong could be in danger if returned to the country that they fought, unsuccessfully, to keep from falling into communist hands in the 1970s.

Though Thai soldiers were armed with batons and shields Monday, Col. Thana Charuwat said no weapons were used in the repatriation and the Hmong offered no resistance. The last of the group is expected to cross the border early Tuesday.

Many Hmong, an ethnic minority from Laos' rugged mountains, fought under CIA advisers during Vietnam to back a pro-American Lao government _ Washington's so-called "secret war" _ before the communist victory in 1975.

Some dormer American soldiers and civilians who developed close bonds with the Hmong during the war believe that the United States should have done more to help its one-time allies.

Since the war, more than 300,000 Lao, mostly Hmong, are known to have fled to Thailand and for years were housed in sprawling camps aided by international agencies. Most were either repatriated to Laos or resettled in third countries, particularly the United States. Smaller numbers found refuge in France, Australia and Canada.

But now Thailand says it plans to close the camp it emptied Monday. That leaves only some 150 Hmong asylum-seekers known to remain in the country. They are kept in a prison near the Lao border and some of them have threatened suicide if they are returned to Laos. According to recent reports, though, some may be able to resettle in the United States and other countries.

The Thai government claims most of the Hmong are economic migrants who entered the country illegally and have no claims to refugee status.

New York-based Human Rights Watch on Monday called the deportation "appalling" and a low point for Thai Prime Minister Abhisit Vejjajiva's government.

"As a result of what Thailand has done to the Lao Hmong today, Prime Minister Abhisit sinks Thailand's record on contempt for human rights and international law to a new low," said Sunai Phasuk, a Thai representative for Human Rights Watch.

U.S. State Department spokesman Ian Kelly said in a statement that the United Nations and Thailand in the past had deemed that many of the Hmong in this group were "in need of protection because of the threats they might face in Laos."

"The United States strongly urges Thai authorities to suspend this operation," Kelly said.