National police spokesman Prawut Thavornsiri said on Sunday the suspect was part of a people-smuggling gang who helped illegal migrants obtain counterfeit documents, and the bomb attack was in response to a recent crackdown by Thai authorities.

Investigators say he was found with bomb-making equipment and multiple passports.

"The interrogation is not making progress because the suspect is not really giving useful information," Thai army chief General Udomdej Sitabutr told AFP.

"We have to conduct further interrogations and make him better understand so he will be more cooperative — while we have to be careful not to violate the suspect's rights," he added.