Warmbier had entered North Korea as a tourist on a five-day New Year's tour with a group of 20 and was delayed at immigration before being taken away by two airport officials, according to the tour operator that sponsored the trip.
A USA student detained in North Korea has issued a dramatic and emotional apology, confessing in front of cameras his "severe crime", according to state media.
At the government-arranged news conference, Otto F. Warmbier, an undergraduate student at the University of Virginia, said that he tried to steal a banner adorned with a political slogan from Yanggakdo International Hotel on January 1.
People previously held in North Korea have often later recanted their public confessions following their release.
Warmbier, 21, stands accused of a hostile act against the state involving the removal of some kind of political banner from the hotel where he was staying (to show to someone at a church in the United States).
North Korea also alleges that Warmbier met previous year with a member of Z Society, a secretive philanthropic organization at UVA that is known to paint its "Z" symbol around university grounds.
There is speculation that Warmbier's detention could be meant to send a message to the USA and other countries as they deliberate tougher sanctions in response to North Korea's recent nuclear test and rocket launch.
While most tourists to North Korea are from China, roughly 6,000 Westerners visit annually, though the United States and Canada advise against it.
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That official also tells CNN that North Korea believes that Warmbier approached the sign in the middle of the night in an attempt to take it - but that it was larger than he had anticipated, and he was forced to leave it on the floor.
Otto Frederick Warmbier (R), a University of Virginia student who has been detained in North Korea s ... There are allegations that he was manipulated by the US government to carry out the act.
He committed the crime with the connivance of the USA government and the task was given by the Friendship United Methodist Church, which promised him a good reward in return, he said.
Warmbier said he was asked by members of his church to steal a banner.
In a statement provided by the University of Viriginia, Mr Warmbier's father, Fred Warmbier, said: "You can imagine how deeply anxious we were and what a traumatic experience this has been for us".
"I don't have any comment at this time", he told The Associated Press.
Warmbier said he accepted the church's offer because it his family faced "severe financial difficulties" and it was a "golden opportunity to earn money".
US tourism to North Korea is legal and virtually all Americans who make the journey return home without incident. The U.S. State Department has warned against travel to the hermetic country.