A University of Virginia student honored as an “intellectual risk-taker” has been arrested in North Korea, its state-run media said Friday, accusing the American of an unspecified “hostile act” against the state.

Otto Frederick Warmbier, 21, was detained Jan. 2 at Pyongyang airport as he prepared to leave after a five-day trip over the New Year’s holiday, said Gareth Johnson of Young Pioneer Tours, the agency that organized the trip.

This was four days before North Korea conducted its latest nuclear test, and makes Warmbier the third Westerner known to be held in North Korea — a move that is certain to elevate already-high tensions with Washington.

But Warmbier’s detention was not made public until Friday, when the official Korean Central News Agency said it was questioning him about taking part in “anti-state activity.”

The brief statement gave no further information about the accusations or the current status of the student.

Warmbier, it added, “was arrested while perpetrating a hostile act against the DPRK after entering it under the guise of tourist for the purpose of bringing down the foundation of its single-minded unity at the tacit connivance of the U.S. government and under its ma­nipu­la­tion.”

Details of Warmbier’s trip to North Korea were not immediately clear. But the Cincinnati area native loved to travel.

At the university — where he majors in economics — Warmbier was selected as an Echols scholar, a special four-year academic program for fewer than 250 students in each class. Those chosen are described as “intellectual risk-takers” who have shown “academic excellence, intellectual leadership, and evidence of the ability to grapple with complex topics,” according to the university’s website.

“We are certainly eager to have him return to the university,” Abraham Axler, president of the university’s student council, said of Warmbier, who also serves on the council. Warbier is a much-admired junior, he said. “He’s a vivacious, kind and involved member of our community.”

He’s buoyant, a longtime friend said immediately when asked about him. Warmbier wasn’t the class clown – he was way too earnest about academics for that – but he had a goofy, funny side. He seemed infused with happiness, one of those people who never let it show if he had a bad day.

Small American flags have been placed in the trees in front of the Warmbier family home in Wyoming, Ohio. (Gary Landers/AP)

“Always bright and energetic and positive, very passionate about school and very hard-working,” a friend said. “He felt unstoppable.”

A big guy, tall, a runner, a high-school soccer player and swimmer, friends said he is loud – a big presence, but never an intimidating one. He’s just happy, a friend said, very popular in a welcoming way, always ready with a grin and kind words.

Friends interviewed Friday agreed to speak on condition of anonymity because Warmbier’s family has told them they have security concerns related to his detention.

A longtime friend of the family described Warmbier in an email as “exceptionally smart” and “atypically mature, sane, polite, and reasonable. He’s a top notch person. … I have known Otto all of his life, and have never known him to make an unwise decision.”

He always has been a driven student; he used to do all of his homework as soon as he got home from school on Fridays, a friend said.

He was a top student at Wyoming High School, a small well-regarded public school in an affluent part of Cincinnati. He was chosen to be Homecoming King by his classmates in 2012, and was one of three commencement speakers when he graduated in 2013, an honor given based on academic performance and character.

Warmbier advocated for environmental changes on campus, such as hand dryers in bathrooms, and helped manage the $20,000 portfolio for the Alternative Investment Fund, a finance group, according to his profile on Linkedin; rap music, vintage clothes and travel were listed as interests.

Warmbier's Facebook page shows him driving a vintage car in Havana last May. His most recent profile photo — posing with a cow — was captioned: “One picture that captures my compassion for animals, worldly travels, and designer sunglasses... ? Woah.”

“He’s inspiring,” a longtime friend of the family said. “I just don’t think he would ever consider that anything bad would ever happen to him. I don’t think it would enter his consciousness.”

Young Pioneers, one of the handful of tour companies that operate in North Korea, acknowledged that Warmbier was on one of its tours. Photos posted by the group showed New Year’s fireworks — presumably attended by Warmbier and fellow tour members — at the main square in North Korea’s capital, Pyongyang.

“We can confirm that the reports that one of our clients is being detained in Pyongyang are true,” said a statement from the company, which specializes in budget travel.

In Washington, State Department deputy spokesman Mark Toner said officials are aware of media reports that a U.S. citizen was detained in North Korea.

“The welfare of U.S. citizens is one of the Department’s highest priorities,” he said, adding that the Swedish Embassy was helping. “We have no further information to share due to privacy considerations.”

Sweden represents American diplomatic interests in North Korea in the absence of direct ties with the United States.

Ohio Gov. John Kasich, a Republican presidential candidate, called the arrest “inexcusable” and called for Warmbier’s immediate release.

Johnson, the tour group spokesman, declined to comment on the possible reasons for Warmbier's detention. A spokesman for the University of Virginia said representatives had been in touch with Warmbier's family and had no additional comment.

The detention coincides with a period of heightened tensions between Washington and Pyongyang.

Earlier this month, North Korea conducted its fourth nuclear test, sparking international condemnation and leading to efforts to impose new sanctions on the regime. The latest arrest will stoke speculation that Pyongyang wants to use the detainees as bargaining chips to water down the punishment for that test.

The Korean Peninsula has been in a technical state of war since the 1950-53 Korean War ended with an armistice rather than a peace treaty, and some 28,500 American troops are stationed in South Korea.

In recent years, North Korea has taken a number of Americans into custody, often for activities related to spreading Christianity and often only releasing them when a high-profile dignitary visits Pyongyang.

"We don't have enough information about this case, but it's always a risk for any U.S. citizen to go to North Korea," said John Delury, an American international relations expert who teaches at Yonsei University in Seoul. "You have to be careful in a way that we wouldn't think of as normal."

In earlier messages, the U.S. State Department has warned that “U.S. citizens have been subject to arrest and long-term detention for actions that would not be cause for arrest in the United States or other countries." Being on a tour does not make visiting safer, the advisory says.

But in the frequently asked questions on its website, Young Pioneers answers a question about safety in North Korea by saying: “Extremely safe!”

“Despite what you may hear, North Korea is probably one of the safest places on Earth to visit. Tourism is very welcomed in North Korea, thus tourists are cherished and well taken care of,” the travel agency says.

“We have never felt suspicious or threatened at any time. In fact, North Koreans are super friendly and accommodating, if you let them into your world. Even during tense political moments tourism to the DPRK is never affected,” the site said.

North Korea, which is trying to promote tourism partly as a way to earn foreign currency, dramatically eased restrictions on American tourists in 2008, allowing for more Americans to visit at more times of the year.

But as the number of tourists into the isolated state has increased, so too have the number of problems.

Merrill Newman, an 85-year-old Korean War veteran, was detained at the end of a tour in 2014 and held for more than a month on charges of committing war crimes. It transpired that Newman had talked about his service and expressed a desire to meet relatives of the anti-Communist soldiers he had helped train.

Also that year, North Korea held Jeffrey Fowle, a 56-year-old public worker from Ohio, for five months after he left a Bible in a restroom at a seamen’s club in the northeastern city of Chongjin. He was released in October 2014 under “special dispensation” of Kim Jong Un, after negotiations involving Bill Richardson, a former American ambassador to the United Nations with a history of dealing with North Korea.

The following month, two other Americans were released when James Clapper, the Director of National Intelligence, went to Pyongyang. Matthew Miller, a tourist who ripped up his visa upon arrival in Pyongyang, and Kenneth Bae, a Korean-American missionary, had both been serving multi-year sentences in North Korean labor camps.

North Korea is currently thought to be holding two western citizens.

One is a man who identified himself as Kim Dong Chul and said he was a naturalized American citizen who used to live in Fairfax, Va., when he was presented to CNN earlier this month. "I'm asking the U.S. or South Korean government to rescue me," Kim, 62, told the network.

The other is Lim Hyeon-soo, a 60-year-old South Korea-born pastor from Toronto, who has been convicted of committing “activities against” North Korea and sentenced to life serving hard labor.

Nick Anderson, Anne Gearan, Justin Moyer, Brian Murphy and T. Rees Shapiro in Washington, and Carol Morello in Davos, Switzerland, contributed to this report.