Four South Korean “unification activists” met with North Korean agents overseas over several years and helped them carry out intelligence activities and other missions, according to Seoul prosecutors.

The Seoul Central District Prosecutors’ Office said in a release Wednesday afternoon that they indicted the four South Koreans for violating the laws on national security.

The four formed an underground organization called the People’s Unification Front and together worked with North Korean agents they met in Cambodia and Vietnam on several occasions dating from 2016.

Prosecutors saw that the People’s Unification Front was led by the 60-year-old president of a local shoemaking company. In June 2019 in Cambodia, he and another member of the organization, a 44-year-old woman, received $7,000 from North Korean agents as a payoff for their role in the intelligence operations. The two also submitted a written pledge of their loyalty to the Kim Jong-un regime.

The head of the organization’s activities in South Korea’s southwestern provinces, a 58-year-old man, communicated with authorities in North Korea at least 19 times between August 2018 and October 2022, prosecutors found. He waged a one-person anti-North Korea propaganda campaign in May 2021, at the instruction of North Korean authorities.

Prosecutors said that a 55-year-old man leading the organization’s activities in Seoul area also came into contact with North Korean agents in Cambodia in July 2017. He exchanged communications on at least 10 different occasions between May and November 2022.

Prosecutors believe the People’s Unification Front is linked to North Korea’s bureau overseeing espionage against South Korea.

Prosecutors found that the organization was behind anti-US protests, including protests against US-South Korea joint military exercises, and other protests against the ruling conservative political party.

According to prosecutors, the National Intelligence Service has been tracking the organization since May 2016. The police, together with the intelligence agency, conducted a first search of the homes and offices of the organization’s members in November.

Before their indictment on Wednesday, the four were arrested on Jan. 28. Their request to be released was rejected by the court on Jan. 29.