NARATHIWAT : Security officers have arrested two suspects believed to be among more than 25 militants who attacked a military outpost in Rueso district on Tuesday, killing three people and wounding six.

The suspects were detained during a manhunt launched after the attack. Col Pramot Phrom-in, deputy spokesman for the Internal Security Operations Command's Fourth Region, said officials had "clear evidence" the two were involved.

He did not provide any further details.

He said investigators believed all the attackers belonged to the same group of rebels who had attacked the 15,121st Company, known as the Phra Ong Dam military base, in Rangae district in the same province on Jan 19 last year.

One suspect in the Phra Ong Dam case was identified as Sunkipli Sika who was arrested in February this year, Col Pramot said.

On Tuesday, men in uniform similar to that of military rangers arrived at the outpost of the 15,123rd Company in Rueso district in two pickup trucks and three motorcycles before launching a grenade and firing a small gun at soldiers and civilians there.

Village defence volunteers and residents nearby helped the troops and returned fire at the assailants.

Pvt Salawut Minsayom and two villagers, Hio Roipariwat and Nitisak Kwanwichan, were killed in the five-minute gunfight.

Police believed two of the attackers were also killed and their bodies taken away by their fellow assailants in the pickup trucks as they fled the scene. The group left their motorcycles behind.

According to an investigation, one of the motorcycles belongs to Ahama Tole, a key subordinate of militant suspect Ropaeing Useng.

The militant put the licence plate of a motorcycle registered in Yala over the one used in the attack to cover its original registration, police say.

Police are looking for the hideout of Mr Ahama who is believed to have fled to Yala's Muang district.

They are also looking for the owners of the other two motorcycles left at the scene after finding their licence plates had been switched.

Investigators believed militants from tambon Lalo and Rueso in Narathiwat and tambon Chakwa in Yala's Raman district joined in the attack. Most are wanted on insurgency-related charges.

The army had been aware of the possibility of increased insurgent violence before the Muslim fasting month of Ramadan which begins tomorrow.

"I learned from an intelligence report around noon [on Tuesday] that the attack would occur within two days," Deputy Prime Minister Yutthasak Sasiprapa said.

The attacked outpost also served as a checkpoint, he said.

The deputy prime minister said he now planned to visit the South.

"We need to go down there to discuss new strategies," he said. "The rebels are not stronger but they have joined forces to stir up violence ahead of Ramadan."