Kim Hak-tune worked at the Pyongyang University of Science and Technology (PUST) and was hung on 6 May, state-run news office KCNA said.
The US has in the past blamed North Korea for confining its nationals to utilize them as pawns.
KCNA said that "a significant foundation" was "leading [a] definite examination" into Kim Hak-tune's claimed wrongdoings.
It gave no further subtle elements.
A State Department official said Washington was "mindful of reports that a US subject was kept in North Korea", including it would liaise with the Swedish Embassy in Pyongyang, which takes care of US interests in North Korea.
Kim Hak-tune had beforehand depicted himself as a Christian evangelist who planned to begin a trial cultivate at PUST, Reuters news organization detailed, refering to an online post by Mr Kim.
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