BANGKOK  In a quick, one-day operation, Thai soldiers with riot shields and clubs evicted more than 4,000 Hmong asylum seekers from a holding center Monday and forcibly repatriated them to Laos, where they say they face retribution from their government.

“They have been sent on their way back to Laos,” said the government’s chief spokesman, Panitan Wattanayagorn. “They have officers waiting for them in Laos already, and Thai officers are accompanying them in the process.”

Thailand acted despite protests from the United Nations and human rights groups. Even as the soldiers were trucking the Hmong over the Mekong River into Laos, the United States government was calling on the Thai government to stop.

“We deeply regret this serious violation of the international humanitarian principles that Thailand has long been known for championing,” said a State Department spokesman, Ian C. Kelly. “The United States strongly urges Thai authorities to suspend this operation.”