Police detained 531 men,in Sunday's raid at a camp near the town of Sadao in the southern province of Songkhla, on a well-established route for human smugglers near Thailand's border with Malaysia. It was the first raid on illegal Rohingya smuggling camps since January 9, 2013.
The police said they were following up on a December 5 Reuters report that Rohingya were held hostage in camps hidden near the border withuntil relatives pay ransoms to release them. Some were beaten and killed.
The Rohingya are mostly stateless Muslims from Myanmar, also known as Burma. Deadly clashes between Rohingya and ethnic Rakhine Buddhists erupted in Buddhist-majority Myanmar last year, making 140,000 people homeless, most of them Rohingya.
The United Nations and the United States called for an investigation into the Reuters report, based on a two months of research in three countries, that revealed a clandestine policy to remove Rohingya refugees from Thai immigration detention centers and deliver them to human traffickers waiting at sea.
"After Reuters gave us information, we ordered an investigation into the camps," said Chatchawan Suksomjit, deputy national police chief. He said they captured threeringleaders at the camp, all of them Thai males.
Reuters gave the Thai authorities coordinates to one camp near Sadao which was empty by the time they arrived, but police found another camp nearby.
"From the Reuters report, we received a clue that it was in Kao Roop Chang (village). But the camp was already moved from there when we found it. We found only an empty camp there. So we investigated more until we found the new camp," said Colonel Kan Tammakasem, superintendent of immigration in Songkhla.
The plight of the Rohingya illustrates the limits to Myanmar's wave of democratic reforms since military rule ended in March 2011. Inside Myanmar, they face apartheid-like conditions and, according to the United Nations, many forms of "persecution, discrimination and exploitation".
Police are trying to identify the origins of those detained after the raid, not all of whom were Rohingya, said Chatchawan. "We are interviewing all of them to see if they are victims of human," he said.
They are being kept at an immigration detention center in Songkhla.
"We have to interview them and proceed according to Thai immigration laws," he said. "It will depend on whether they want to go back. If they are willing we will send them back as we have done before."
Last year, Thailand implemented a secretive policy to deport the Rohingya.
These deportations delivered many Rohingya back into the hands of smuggling networks and human traffickers, who in some cases ferried them back to Thailand's secret border camps, reported Reuters.
The raid comes as the U.S. State Department is finalizing its research for its next Trafficking In Persons (TIP) report, due in June, which ranks countries on their counter-trafficking performance.
Thailand is Southeast Asia's second-biggest economy and a close U.S. ally, but has a poor record in fighting trafficking and faces a possible downgrade to the report's lowest rank, putting it at risk of U.S. sanctions and potentially placing it on a par with North Korea andIran.
Nine people were arrested in Thailand in relation to Rohingya smuggling in 2013, including two government officials, according to police data, but none of the arrests has led to convictions.
(Additional reporting by Jutarat Skulpichetrat; Editing by Jason Szep and Robert Birsel)