Investigators said the the attack was motivated by a "family conflict", not organised crime.
Robbers entered the police station in the southern village of Engcobo shortly after midnight, opening fire on the officers and seizing two others, who were later shot and killed, police spokesman Vish Naidoo said.
The General Authority of Customs (GAC) has foiled a number of attempts to smuggle illicit drugs and banned firearms into the country, it was announced on Sunday.
Belgian prosecutors said on Wednesday they had charged two Belgian nationals with terrorist activity after police found weapons and detonators during house searches overnight in the capital Brussels.
Malaysian authorities have arrested six local men for suspected involvement with the Islamic State militant group, police said on Saturday.
Kenya destroyed some 5,250 illegal firearms by fire on Tuesday as part of efforts to fight crimes like cattle rustling, carjackings and to eliminate threats from terrorism.