Police believe six men, including two already questioned and discharged, were involved in Saturday's Narathiwat hotel bomb blast.
The blast on the third floor of the Asia Hotel on Charoen Khet Road in Sungai Kolok municipality wounded six people. The injured victims are now out of danger.
After the explosion, police rounded up Sulaiman Yapa and Tameesi Jeyor, both 19, from Narathiwat's Sukhirin district.
The pair, who had stayed at the hotel the previous night, were seen on surveillance camera footage rushing out of the hotel shortly before the blast.
The suspects told police they hurried out of the hotel to catch a bus.
The pair were released later on Saturday after police took their fingerprints and DNA samples.
Four other men, who had checked in to rooms close to the blast, were also taken in for questioning by authorities at the 46th special ranger unit in Narathiwat yesterday.
Pol Maj Kitti Mankong, inspector of Muno police station in Sungai Kolok, said investigators had found the four men _ identified by police as Abu Nigumrai, Nasueree Daemoleng, Adeeyas Jesu and Rustan Dorlor _ had been in contact with Mr Sulaiman and Mr Tameesi before.
Police also searched a house in tambon Muno of Sungai Kolok where the four men reportedly lived.
Narathiwat governor Aphinan Suethanuwong said authorities believe all six men were involved in the explosion.
Police will collect more evidence before pressing charges, he said.
Meanwhile, police found and safely detonated a bomb stuffed inside a gas cylinder weighing more than 30kg under the surface of the Donna-Bang Tan rural road in tambon Bangkao of Pattani's Nong Chik district at 9am yesterday.