Radio Free Asia(RFA) reported Tuesday that North Korea’s State Security Department has arrested about 300 North Koreans on charges of being involved in an espionage case in North Hamgyeong Province.

A local source said in an interview with RFA that the department had warned people to turn themselves in within a week if they are contacting family members who defected to South Korea or selling state secrets to the South for money, but no one came forward.

The department then reportedly arrested over 30 North Koreans in one day on charges of espionage in the northern part of the province.

The source claimed that the department even arrested residents in the South Hamgyeong, South Pyongan and North Hwanghae provinces and tortured and grilled them.

RFA said that the arrests came after the department had found a critical document in a search of the house of a North Korean woman, who reportedly defected while working as a broker to help North Korean defectors send money to their families in the North.

RFA said that the truth will soon come out whether the department is seeking to eliminate a certain organization on the pretext of the document of the broker, or sever North Korean residents’ connection with South Korea by creating fear among people.