South Korea on Monday urged Pyongyang to release four of its citizens being held by the North, including two men who told CNN they spied for the South, and a 21-year-old New York University student.
Two men arrested by North Korea in March said in interviews with CNN that they spied for South Korea's intelligence agency, but the cable television news network said it could not verify their accounts.
North Korea said Kim Kuk-gi and Choe Chun-gil were South Korean nationals working as spies for Seoul's National Intelligence Service (NIS) from the Chinese border city of Dandong.