Thailand's army chief on Sunday told AFP the man arrested in connection with last week's deadly Bangkok bomb blast was not cooperating, as police announced he was part of a people-smuggling gang.
The unnamed foreigner, who is being held in military custody at an undisclosed location, was seized during a Saturday morning raid on a flat on the eastern outskirts of Bangkok.
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.
The blast that hit the Erawan shrine in a busy Bangkok shopping district on August 17 was Thailand's worst single mass-casualty attack, killing 20 people, most of them ethnic Chinese tourists from across Asia.
Police and the junta have been keen to play down any suggestion the attack was launched by international terrorists or specifically targeted Chinese tourists.
National police spokesman Prawut Thavornsiri said 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.
"They (the gang) are unsatisfied with police arresting illegal entrants," he told Channel 3 in a telephone interview.
"He (the suspect) had more than 200 fake passports (when he was arrested). It's a network that fakes nationalities and sends them (illegal migrants) on to third countries," he added, without elaborating how he received that information.
Bangkok has long had a reputation for gangs that produce counterfeit documents, while Thailand has been a major regional hub for both people smuggling and trafficking.
For days Thai police have been searching for a network believed to be behind the Erawan shrine attack and another blast the following day by a busy commuter pier that caused no injuries.
The investigation has focused on a prime suspect, described as a foreign man, who was captured on security footage wearing a yellow t-shirt and leaving a bag at the shrine moments before the blast.
But authorities have not yet said whether they believe the suspect now detained is the same as the man seen in this video footage.
Udomdej told AFP he believed the arrested man was "absolutely involved with the bombs" adding that his physical appearance "looked like" the suspect seen in CCTV footage.
"But I will not determine whether he is the bomber or not," he added.