According to Kim Mi-ok, Kim Hak-song had been teaching agricultural techniques at Pyongyang University for Science and Technology and did not engage in any missionary work.
North Korea said Kim Sang-dok was arrested "for committing criminal acts", but did not elaborate.
"Professor Kim was a man who would call North Korea as his own country".
Since the USA and North Korea do not hqve diplomatic relations, when an American citizen is reported to be detained, the US works with the Swedish embassy in Pyongyang.
Kim Hak Song, who worked for the Pyongyang University of Science and Technology, was detained on Saturday, the North's KCNA news agency said. USA tourist Otto Warmbier is serving 15 years imprisonment with hard labor over the theft of a political propaganda poster in January 2016 and Kim Dong Chul, a Korean-American businessman, is serving 10 years on espionage charges.
"South Korea and the USA agree that now isn't the right time for talks" with North Korea, the official said, highlighting Pyongyang's ceaseless threats to carry out a nuclear attack.
The wife of a US citizen who was detained in North Korea over the weekend is appealing for his immediate release.
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In 2014, the Obama administration sent Director of National Intelligence James R. Clapper on a secret mission to North Korea to retrieve two US citizens who had been detained by North Korea.
"Foreign nationals in the DPRK really have to allow for there to be no ambiguity or interpretation about any of their interactions or what they're doing", says Madden, a contributor to North Korean monitoring organization 38 North.
Citing unidentified diplomatic sources, the Japanese newspaper wrote that in return for North Korea foreswearing its nuclear and missile technologies, the USA promised it "would not seek regime change, regime collapse or an accelerated reunification of the Korean Peninsula, nor would it look for an excuse to advance north of the 38th parallel, the de facto inter-Korean border".
PUST is North Korea's only privately funded university and has a large number of foreign teachers, including Americans.
Another American citizen has been taken hostage by North Korea.
"Because no American president is going to let a reckless slightly unhinged North Korean leader get a nuclear weapon capable of reaching the United States".
The North Korean reports also said a "Korean-style anti-terrorist attack" would begin immediately. "Will Kim increase his internal purges of North Korean elites?"
Last year's party congress, the first one in more than 30 years, was a venue for Kim to reaffirm his unfettered rule.