A North Korean agent disguised as a defector has been detained on suspicions of violating South Korea's National Security Law, Seoul's prosecutors said Tuesday.

During a routine investigation of newly arrived defectors that was held recently, the 50-year-old suspect surnamed Kim reportedly confessed that he is a spy working for the North's National Security Agency, according to prosecutors.

South Korea's National Security Law prohibits its citizens from contacting North Koreans without government approval and engaging in activities benefiting the North.

In June, Kim entered South Korea after posing as a North Korean defector in an attempt to collect information on defectors in the South, prosecutors said. Before coming to Seoul, Kim had carried out espionage activities for the North's spy agency in China for 15 years.

Prosecutors said they have requested a warrant to arrest Kim on Friday on suspicions of spying for the communist regime and a court will soon decide whether to approve the warrant.

The arrest is the latest case showing that Pyongyang is still attempting to infiltrate spies into Seoul, home to more than 24,000 North Korean defectors.

In July, prosecutors indicted a North Korean female agent on charges of working for another major North Korean spy agency, the State Security Ministry. (Yonhap)