South Korea on Jan. 26 rejected allegations that Seoul was supporting an anti-Pyongyang campaign through missionaries based in China.
"We express strong regret that the truth is being distorted, while our national is being detained for a long period," Seoul's Unification Ministry said, AFP reported.
Kim Kuk-gi, one of three South Koreans currently held in the North, was shown in a video delivering what appeared to be a scripted confession that said Seoul was behind the spying plot.
Kim was sentenced in June 2015 to life imprisonment with hard labor on charges of spying for South Korea's intelligence service.
Kim admitted to distributing forged video clips of torture by the North Korean government and luring defectors to cross the Chinese border.
He said a handful of South Korean Christian groups were actively involved in this "smear campaign" orchestrated by the South Korea's National Intelligence Service.