Move comes despite international concerns that they will face persecution in their home country
The Thai government rejects accusations by the international community that thousands of Lao Hmong refugees were being forcibly sent back to Laos. The Thai military carried out the deportation under tight security.
The deportation of 4,000 Hmong to Laos began in the early hours of Monday with convoys of military trucks and buses ferrying people to the border.
Human rights groups fear the Hmong, who have been held at the Huay Nam Khao refugee camp, will be persecuted once they return to Laos.
The U.S. government called for a suspension of the operation, saying Thailand has violated international humanitarian principles by forcibly returning the Hmong.
Thai government spokesman Panitan Wattanayagorn denies that accusation. He says Lao authorities promise to grant amnesty to those returning.
"No, no, not forcefully - they volunteer to go back at least in the morning of today," he said. "Many of them are on the way back and those who are they have told the officers' in charge they have told us that they are volunteer[ing] to go."
He says under Thai law the Hmong are illegal immigrants and they have been treated according to law.
"We do this in good faith. … We have to follow the compliance with human rights standards and we have to make sure these people will be repatriated back in safe and sound condition," he said.
But the United Nations' High Commission for Refugees says several in the camp would have qualified as refugees. Thailand never allowed the UNHCR or any other groups to assess the status of the Hmong in the camp.
The Human Rights Watch representative in Thailand, Sunai Pasuk, calls the repatriation a "serious breach in international standards".