Sub-Lt Marorseh Muna, 45, an investigator at Muang Pattani police station, was slain on Saturday morning.
A defence volunteer was wounded in the same incident in Muang district, said Pol Col Tuande Juthanant, the chief of Muang Pattani police.
Witnesses told police that Sub-Lt Marorseh was drinking tea inside a teashop at Moo 2 in tambon Bana when four men arrived on two motorcycles. A gunman riding pillion on one motorbike fired at him with a handgun. The attackers then fled.
Sub-Lt Marorseh took three bullets in his head and torso and died on the spot.
Volunteer Isamaeh Masae was shot in his left arm and taken to Pattani hospital.
The incident followed the slaying of a territorial defence volunteer in a drive-by shooting on Friday night in Nong Chik district of Pattani.
The dead man was identified as Jehusman Hayikaseng, 46, of Muang Pattani district.
Pol Lt Chaiyan Bandith, the duty officer at Nong Chik police station, said the shooting occurred about 7pm on the Don Rak-Tha Dan road at Ban Don Rak in Tambon Don Rak.
According to witnesses, Jehusman was travelling along the road when a gunman riding pillion on another motorcycle fired at him with a handgun. The assailants then fled.
Jehusman took two bullets in his chest and died on the spot.
Almost 6,000 people have been killed in the southern violence since Jan 4, 2004 which marked the re-emergence of separatist unrest, according to the Internal Security Operations Command Region 4 Forward Command.
A total of 5,926 people have died as a result of sectarian violence in Yala, Pattani and Narathiwat as well as Chana, Thepha, Saba Yoi and Na Thawi districts of Songkhla up to Dec 31 last year, official statistics show.
Of the dead, 3,461 were Muslims and 2,431 were Buddhists. A total of 10,593 people have been injured.