A manhunt for six suspects accused of killing two police officers in Narathiwat has intensified after investigators found evidence suggesting they may have fled across the border.

The search followed the attack shortly before noon on Sunday at a palm plantation behind the Priwan tambon administrative organisation (TAO) in Tak Bai district.

That resulted in the killing of Pol Sgt Maj Hamran Ha and Pol Sen Sgt Maj Withaya Chaipromkaew, injuring four other police officers, all stationed at Tak Bai Provincial Police Station.

According to a source, authorities are confident the suspect who shot the investigating officers is a man known as Arif, a fugitive wanted on drug charges.

He is also believed to be involved in and aware of the previous case of a car bomb attack in front of the old Tan Yong Police Station.

He was possibly involved in another car bomb attack on a vehicle carrying volunteer defence personnel from Sungai Kolok district returning from refresher training in Yala province. The bomb missed its target but hit a Malaysian tourist's car, injuring two Malaysians.

They were also able to identify at least six assailants, three of them are on arrest warrants in other cases, police said. The six are now thought to be hiding out in a neighbouring country.

Evidence collected at the palm plantation where the assailants were believed to have been positioned during the attack included 24 M16 bullet casings, 21 9mm pistol bullet casings, one .32 calibre bullet casing, and a disassembled HK rifle, along with various personal items, a shoulder bag, a field stretcher, and a knife.

Meanwhile, assailants opened fire at the Pattani Area Excise Office, Mayo Branch, before noon on Tuesday, injuring one person and damaging the office building.

Preliminary investigation revealed that, prior to the incident, police officers and excise officials had arrested a suspect in Sai Buri district, Pattani province, for allegedly selling untaxed cigarettes.

The suspect was subsequently taken to the Pattani Area Excise Office, Mayo Branch, for legal procedures related to a fine.

Approximately 10 minutes after arriving at the office, two assailants riding a motorcycle approached the front of the building. They then opened fire on the office before fleeing the scene.

Following the attack, authorities secured the area, provided assistance to the injured victim, and began collecting evidence. Investigators are reviewing CCTV footage and pursuing the suspects.