North Korea is denouncing South Korea for making what it calls fabricated spying accusations.
The Secretariat of the Committee for the Peaceful Reunification of Korea blasted South Korea in a statement Thursday for "cooking up" the espionage claims.
The statement carried by the official Korean Central News Agency said, "The 'spy ring case' is a groundless farce."
South Korean prosecutors said Monday that five South Koreans had been arrested on suspicions of forming an underground organization to supply military secrets and other information to the North.
The two sides periodically trade spying allegations.
The Korean peninsula remains in a technical state of war because the Korean War ended in a truce instead of a peace treaty in 1953.