SEOUL (Reuters) – North Korea has detained a U.S. university student, the third western citizen known to be held in the isolated state, for committing a “hostile act” and wanting to “destroy the country’s unity”, it said on Friday.

Otto Frederick Warmbier, 21, of the University of Virginia, was in North Korea for a five-day New Year trip and was detained at Pyongyang airport on Jan. 2 ahead of a flight back to China, said Gareth Johnson of Young Pioneer Tours, which organized the visit.

According to the North’s official KCNA news agency, 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 U.S. government”.

The U.S. State Department, in a statement, said it was aware of reports that a U.S. citizen had been detained in North Korea but gave no other details, citing privacy concerns.

Johnson said China-based Young Pioneer Tours was in contact with Warmbier’s family and U.S. officials.

“We are in touch with Otto’s family, the U.S. State Department and the Embassy of Sweden in Pyongyang and doing all we can to secure his release,” Johnson told Reuters.

The Swedish Embassy represents U.S. interests in North Korea.

KCNA said Warmbier had entered the country with an “aim to destroy the country’s unity”. It did not elaborate.

According to his social media profiles, Warmbier is from Cincinnati and is an Echols Scholar, awarded to the top seven percent of incoming first year students at the University of Virginia, where he majors in economics with a minor in global sustainability.

Warmbier has also visited Cuba, Ireland and Israel, according to his Facebook profile.

Warmbier was detained four days before North Korea conducted its fourth nuclear test in violation of UN sanctions, which drew condemnation from its neighbors and the United States.

South Korea warned that the United States and its allies were working on further sanctions to inflict “bone-numbing pain” on North Korea after its latest nuclear test, and urged China to do its part to rein in its neighbor.

North Korea has a long history of detaining foreigners, and the U.S. and Canadian governments advise against travel there.

Pyongyang has in the past used detained U.S. citizens to extract high-profile visits from the United States, with which it has no formal diplomatic relations.

While the vast majority of tourists to North Korea are from China, roughly 6,000 westerners visit the country annually. Most are adventure-seekers curious about life behind the last sliver of the iron curtain, and ignore critics who say their dollars prop up a repressive regime.

Warmbier was on Young Pioneer’s “New Year’s Party Tour”, which, according to the itinerary on the company’s website, was to include watching fireworks in Kim Il Sung Square in the heart of Pyongyang, and an optional helicopter ride.

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 that he was being held by the state for spying.

In 2014, Pyongyang released three detained Americans. Last October, it freed a South Korean national with a U.S. green card after holding him for six months.

(Additional reporting by Christine Kim and Se Young Lee in Seoul and David Brunnstrom in Washington; Writing by Tony Munroe; Editing by Nick Macfie)