Thai soldiers head to a refugee camp in Phetchabun province early Monday as an operation gets underway to expel about 4,000 ethnic Hmong back to Laos. (Sakchai Lalit/Associated Press)

Thai troops packed more than 4,000 ethnic Hmong into military trucks for a one-way journey to Laos, ignoring pleas from the United States and human rights groups that they could be in danger.

The European Union said it was "deeply dismayed" by the forcible deportation and issued a statement that urged Laos to ensure the Hmongs' human rights are protected and international observers are granted "unfettered access" to them.

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 crossed the border early Tuesday.

Hmong hill tribe people fought on the side of a pro-American government during the Vietnam War, but Lao communist forces — known in the West as the Pathet Lao — emerged triumphant in 1975.

Thailand claimed most of the Hmong at the refugee camp had no legitimate claim to refugee status but were simply economic migrants who entered the country illegally.

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're kept in a prison near the Lao border and some of them have threatened suicide if they are returned to Laos.

With files from The Associated Press