Prosecutors in South Korea have charged five men with spying for North Korea.
The South Korean men are alleged to have passed military and political information to the Communist north over the past 20 years, the BBC reports.
Prosecutors say the men passed on satellite images of major military installations, field manuals of US forces in South Korea and information on politicians from both the ruling party and the opposition.
One of the men is a former parliamentary aide.
The suspected ringleader, known as Mr Kim, was alleged to have operated in South Korea under a code name, setting up what prosecutors described as "an anti-national organisation" to send information back to the North.
He was said to have met North Korea's late founding father, Kim Il-sung, in 1993.
Two other men are alleged to have been responsible for reporting from Seoul and from the area of Incheon just outside the capital, where South Korea's main airport is based.
Officials say they believe North Korea was focusing many of its operations there, with the aim of using the Incheon region as a bridge to infiltrate the country in the future.