North Korea claims to have detained a US university student for committing a "hostile act" and wanting to "destroy the country's unity".
If so, Otto Frederick Warmbier would be the third western citizen known to be held in the isolated state.
The state-run KCNA news agency said on Friday Warmbier entered North Korea as a tourist and "was caught committing a hostile act against the state", which it said was "tolerated and manipulated by the US government".
The agency said Warmbier had entered the country with an "aim to destroy the country's unity". It did not elaborate.
Warmbier is an undergraduate at the University of Virginia, according to the university's website.
Gareth Johnson of China-based Young Pioneer Tours confirmed Warmbier was on one of its tours and said he had been detained in North Korea on January 2.
An official at the US embassy in the South Korean capital Seoul said it was aware of the reported arrest.
Johnson said Young Pioneer Tours was in touch with Warmbier's family and US officials.
"We are in touch with Otto's family, the US State Department and the Embassy of Sweden in Pyongyang and doing all we can to secure his release," Johnson said.
The Swedish Embassy represents US interests in North Korea.
A South Korean-born Canadian pastor was arrested in North Korea last year and given a life sentence for subversion. Earlier this month, a Korean-American man told CNN in Pyongyang he was being held for spying.
In 2014, Pyongyang released three detained Americans.
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