South Korea on Monday urged North Korea to identify a South Korean citizen it said it had arrested for espionage, as a newspaper report suggested the detained man was a missionary.
Pyongyang announced last week that it had arrested a South Korean spy engaged in "plot-breeding activities."
The South's National Intelligence Service rejected the claim as groundless, and the Unification Ministry on Monday challenged the North to provide information to support the spying charge.
"Since the North has said it is holding a South Korean in custody, we want his identity to be disclosed," ministry spokesman Kim Eui-Do told reporters.
The Chosun Ilbo newspaper in Seoul cited South Korean activists as saying the man was a missionary, who may have entered North Korea with a fake passport after he was told by a contact that he could meet churchgoers there.
Last week, North Korea accused South Korean spies and activists of "abducting" its citizens and vowed to respond with "merciless" punishment.
The North's Committee for the Peaceful Reunification of Korea mentioned South Korea's spy agency chief Nam Jae-Joon by name as its "prime" target.