It's the third American currently held by the authoritarian nation.
State Department spokeswoman Marie Harf is citing privacy reasons in providing no further details.
North Korea's state news agency says the American is tourist Jeffrey Edward Fowle. The agency says Fowl is being investigated for acts inconsistent with the purpose of a tourist visit, and that Fowle entered the country on April 29.
Harf did not identify the latest detainee or say whether Sweden has been granted access to him. Sweden handles consular matters for Americans in North Korea.
Harf says the department has a warning against travel to North Korea. She says being part of a tour group will not protect you from arrest.
The Korean Central News Agency said that authorities were investigating the American for allegedly committing acts inconsistent with the purpose of a tourist visit. It did not give details
KCNA said the American went to North Korea on April 29.
The person would be the third American currently held in North Korea.
In April, North Korea said it had detained a 24-year-old American for improper behavior while he was being processed to enter the country as a tourist. He was identified as Miller Matthew Todd — possibly putting his surname first. It said he entered the country on April 10 with a tourist visa, but tore it up and shouted that he wanted to seek asylum. The brief report said he chose the North "as a shelter."
North Korea has been holding a Korean-American missionary, Kenneth Bae, since November 2012. Bae was sentenced to 15 years of hard labor for what the North says were hostile acts against the state.
In March, North Korea deported an Australian missionary detained for spreading Christianity in the country after he apologized for anti-state religious acts and requested forgiveness.
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