Pattani provincial police commander Major General Panya Thiensart said the attacks in Sai Buri, Yaring, and Nong Chik districts occurred almost simultaneously on Thursday evening.
The unidentified assailants, who were wearing masks, then took two machine guns and a pistol from the victims, he said.
Police have not yet established a motive for the killings but hostility and violence against authorities representing the central government in the region is long-standing.
"They just wanted to kill police, that's all I can say," Panya said.
The civilian was killed at the Sai Buri police outpost when he got caught got in cross-fire.
A government representative said the deaths served as a warning to police that they must be on guard for further attacks.
Police were warned by military intelligence of possible attacks against officers in the south but they could not prevent the incidents because they happened in an unexpected area, he said.
Thailand's five Muslim-majority provinces suffered a spate of violence in 2001 and 2002 during which more than 20 police officers were killed, trains bombed, government offices attacked and weapons depots raided.
Provincial leaders and Islamic authorities at the time blamed criminals fighting over the profits from illegal businesses, rather than the Muslim separatists who have been active in the south for decades.
However, the arrests last month of three Thai Muslims suspected to be members of the Jemaah Islamiyah (JI) group has attracted fresh attention on unrest in the region.