Media reports say a South Korean man arrested this month in Pyongyang is a Christian missionary, who was working there to help North Korean refugees.
The Wednesday reports, by the French news agency and South Korea's Dong-A Ilbo, identified the man as 50-year-old Kim Jeong-Wook.
His family and other Christian activists told the news outlets that Kim had been helping North Koreans who escaped their homeland to China for years.
They say Kim was arrested after traveling to Pyongyang to check on the wellbeing of several refugees who had been repatriated by Beijing.
North Korea said earlier this month it arrested a South Korean "spy" who was engaged in "plot-breeding" activities. It provided no other details.
If confirmed, Kim would join Korean-American Kenneth Bae as the the second Christian missionary recently detained by North Korea on spying charges.
Bae was arrested in 2012 and sentenced to 15 years hard labor for allegedly trying to topple the North Korean government.
The communist North Korean leadership views organized religion as a threat to its hold on power.