No details have been given about the American's identity or the circumstances of the arrest.
The news comes ahead of a scheduled visit to Seoul this weekend by US Secretary of State Hillary Clinton.
Efforts to ease tensions on the Korean peninsula are continuing, after two military attacks last year.
The state department is refusing to answer questions about the detained citizen - such as who are they? What were they doing in North Korea? When, where and why were they arrested? - because it says the individual has not signed a privacy waiver. Read More