BANGKOK, Jan. 14 (Xinhua) -- A police officer was killed when an unknown gunman opened fire at a police station in southern Thailand on Sunday, police said.

Pol. Sgt. Chalermphol Khomkham was pronounced dead on the way to hospital shortly after he was fatally shot by the gunman who was among six men riding on motorcycles outside Na Pradu police station in Khok Pho district of Pattani province, according to provincial police commander Pol. Maj. Gen. Piyawat Chalermsri.

The attack was believed to be launched as a revenge following Saturday's event in which two gunmen were gunned down by police in Pattani, the police general said.

Last Thursday, four security guards were shot by a group of gunmen at a school in the same province. Three of the defense volunteers were killed at the scene while the remaining one was pronounced dead at hospital.

Authorities suspect that members of the separatist Barisan Revolusi Nasional, or the National Revolutionary Front, launch a series of attacks on government employees in the south.