Muang station police were first notified on May 18 when 28 AK102s were found missing from the arms depot of the territorial defence office.
On Tuesday, the police station’s superintendent told the press that his subordinates were checking the number of weapons in each depot of the province.
The latest update showed that nine more rifles have gone missing.
The five districts with the missing rifles are Muang, Su-ngai Kolok, Rue So, Sri Sakhon and Su-ngai Padi.
Security forces have been battling an insurgency in the deep South for nearly two decades.
The police suspect some of the guns could have been stolen by local insurgents as officers had found that the same kind of weapons were used by the insurgents in a shootout on May 11.