Apirak said no other details were immediately available but the authorities suspected the attack was the work of Muslim fighters who wanted to stir up communal tension.
On Wednesday, two civilians were killed and four policemen wounded in the south.
The two Muslim civilians were killed as they left a tea shop in Narathiwat province when four assailants got out of their pickup truck and fired dozens of shots from assault rifles, police Lieutenant Vorapong Klomsakun said.
Policemen injured
In Yala province, a roadside bomb wounded three border patrol policemen who were in a van on patrol duty.
Another bomb, hidden beneath a motorcycle, exploded in front of a school in Narathiwat, wounding one policeman.
The bomb was triggered by a mobile phone, police said.
Meanwhile, three men were arrested in connection with a 30-minute gun battle on Tuesday night in Pattani province, in which three policemen and two suspected fighters were killed, army spokesman Akara Thiprote said.
In a separate raid at a mosque in Narathiwat, the authorities found a cache of camouflage and military-style uniforms, two-way radios, ammunition and maps of government offices.
More than 2,000 people have died since January 2004 in Thailand's southern provinces of Yala, Narathiwat and Pattani as a result of the separatist uprising.
Government measures to quell the violence have failed to gain any noticeable ground.