It was the first clear indication that police believe a group of southern Muslims played some sort of role in the attacks which killed four and wounded dozens, including European visitors, this month.
Police chief Chakthip Chaijinda told reporters investigators believe a group of "more than 20 people" were behind the coordinated attacks.
"Most of them are from the area of the southern border provinces police operation centre," he said, referencing a policing area that encompasses the Muslim-majority southernmost region.
He added that investigators had recently searched an Islamic school where he believed some of the suspects had studied or graduated from.
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More than 6,500 people, mostly civilians, have been killed in 12 years of violence between the Buddhist-majority state and shadowy ethnic Malay Muslim rebels seeking greater autonomy.
But the violence has largely remained local and foreign visitors are also largely insulated from domestic political clashes that have hit the capital.
That changed on 11-12 August when a string of coordinated bomb and arson attacks struck multiple tourist resort towns in Thailand's south.
The junta which seized power in 2014 has been reluctant to finger insurgents in the deep south, suggesting disgruntled domestic opponents instead.
Analysts say the leadership fears any admission that southern insurgents were behind the attack might harm tourism and raise questions over the military's ability to ensure security.
However in recent days the police investigation has increasingly pointed southwards.
One arrest warrant has so far been issued for a named suspect over the attacks, a Muslim man from the southern province of Narathiwat.
At his briefing police chief Chakthip said he was not ruling out any motive, adding that the group "might have been hired" by others to carry out the attacks.
He said he believed the perpetrators were previously unknown to police, not veterans from within the Malay insurgency who might be easier to catch and identify.