Investigators were looking to determine if the bombers may have been involved in the blast that rocked the Central Festival store on Koh Samui last year.

Four police on patrol noticed a man driving a pickup truck to the bomb site and parking it there before jumping on the back of a waiting motorcycle.

The police approached the two men to question them but the suspects did not respond and sped away.

The police gave chase but failed to catch them. A few minutes later, the bomb went off.

“After we received the report on the blast at 6.10am, we rushed to the scene,” Pol Colonel Kong-at Suwankham from Sungai Kolok Police Station said.

By the time they arrived, the pickup was engulfed in flames. Bomb fragments and debris were scattered all around. Two locals suffered minor injuries and were sent to hospital.

Chaiwit Areekoonchai, 40, was hit by shrapnel on his forehead, while Zakirun Mosoh, 19, developed chest pains and ringing in his ears.

After the fire was extinguished, officials examined the scene and found that a part of a wall had collapsed and nearby shops and knockdown housing units were damaged.

Pol Colonel Nitinai Langyanai, deputy Narathiwat police chief, said about 80 kilograms of explosives might have been planted inside the vehicle.

“This pickup was stolen from a beach in Narathiwat two years ago,” he said.

Kong-at identified Suhaidi Kubaru as the pickup driver and Haseuming Puta as his one of his accomplices.

Manop Khemlek, a deputy district chief, said 28 people had sought assistance from authorities after their properties were damaged by the bomb attack.

Songkhla province raised its security readiness to the highest level.

Also in Narathiwat, security officials uncovered a hidden arms cache and plan to examine fingerprints left behind on the items.