An American student held in North Korea since early January was detained for trying to steal a propaganda slogan from his Pyongyang hotel and has confessed to "severe crimes" against the state, the North's official media said on Monday.

Otto Warmbier, 21, a student at the University of Virginia, was detained before boarding his flight to China over an unspecified incident at his hotel, his tour agency told Reuters in January.

North Korea has a long history of detaining foreigners and has used jailed U.S. citizens in the past to exact high-profile visits from the United States, with which it has no formal diplomatic relations.

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"I committed the crime of taking out a political slogan from the staff-only area of the Yanggakdo International Hotel," the North's KCNA news agency quoted Warmbier as telling media in Pyongyang, the North Korean capital.

CNN showed video of a sobbing Warmbier saying: "I have made the worst mistake of my life, but please act to save me."

Warmbier said a "deaconess" had offered him a used car worth $10,000 if he could present a U.S. church with the slogan as a "trophy" from North Korea, KCNA said.

The acquaintance also said the church would pay his mother $200,000 if he was detained by the North and did not return, KCNA quoted Warmbier as saying.

"My crime is very severe and pre-planned," Warmbier was quoted as saying, adding that he was impressed by North Korea's "humanitarian treatment of severe criminals like myself".

Warmbier's family have not heard from him since his arrest, according to a statement provided to the Cavalier Daily, the University of Virginia's student-run newspaper.

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"He seems to be in good health, although we won't know for sure about his condition until we have a chance to speak with him," the statement said.

Other Westerners detained in North Korea previously have confessed to crimes against the state.

North Korea's state media said in January that Warmbier "was caught committing a hostile act against the state", which it said was "tolerated and manipulated by the U.S. government".

The senior pastor at Friendship United Methodist Church in Wyoming, Ohio, told CNN that he did not know the person identified by Warmbier in the KCNA story as a deaconess there, and said Warmbier was not a member of the congregation.

According to KCNA, Warmbier also said he was encouraged in his act by a member of the Z Society, an elite philanthropic organisation at the University of Virginia that he hoped to join.

An official in the university's communications office could not immediately be reached for comment.

Isolated North Korea is expected to face tough new U.N. Security Council resolution following its nuclear test in January and a long-range rocket launch this month.

Warmbier was on a five-day New Year's tour of North Korea with a group of 20 and was delayed at immigration before being taken away by two airport officials, according to a tour operator that had sponsored the trip.

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While the vast majority of tourists to North Korea are from China, roughly 6,000 Westerners visit the country annually, though the United States and Canada advise against it.

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.