SEOUL (Reuters) - North Korea said on Wednesday an American man it had detained in late April, the third U.S. citizen being held by the isolated country, was intercepted because he was attempting to commit “hostile acts”. 
 
 The state-run KCNA news agency said the American, identified last month as Kim Sang Dok, was arrested on April 22 at the Pyongyang airport for committing “hostile criminal acts with an aim to subvert the country”. 
 
 The latest information about Kim’s detention comes as tensions on the Korean peninsula run high, driven by concerns that the North might conduct its sixth nuclear test in defiance of U.S. pressure and United Nations sanctions. 
 
 The United States is negotiating with China, North Korea’s sole major ally, about a stronger U.N. Security Council response, although Washington has also reiterated that all options for dealing with the North remain on the table. 
 
 North Korea, which has been criticized for its human rights record, has in the past used detained Americans to extract high-profile visits from the United States, with which it has no formal diplomatic relations. 
 
 KCNA said on Wednesday Kim had taught an accounting course in Pyongyang. 
 
 “Invited to Pyongyang University of Science and Technology (PUST) to teach accounting as a professor, he was intercepted for committing criminal acts of hostility aimed to overturn the DPRK not only in the past but also during his last stay before interception,” KCNA news agency said, using North Korea’s official name of the Democratic People’s Republic of Korea. 
 
 Law enforcement officials were investigating Kim’s alleged crime, it said. 
 
 Kim, who also goes by his English name Tony Kim and is in his 50s, was detained at Pyongyang International Airport as he attempted to leave the country, the university’s chancellor had said previously. 
 
 PUST said in an email to Reuters that it did not believe Kim’s detention was related to his work at the university. 
 
 A PUST spokesman, who asked not to be identified, said Kim’s wife, who was with him when he was arrested, had since returned to the United States. 
 
 “Mrs Kim left the DPRK and is now back in the USA with family and friends,” the spokesman said. “We certainly hope for a positive resolution as soon as possible.” 
 
 The other two Americans already held in North Korea are Otto Warmbier, a 22-year-old student, and Kim Dong Chul, a 62-year-old Korean-American missionary. 
 
 Warmbier was detained in January 2016 and sentenced to 15 years hard labor for attempting to steal a propaganda banner. 
 
 Two months later, Kim Dong Chul was sentenced to 10 years hard labor for subversion. Neither has appeared in public since their sentencing. 
 
 A North Korean flag flies on a mast at the Permanent Mission of North Korea in Geneva REUTERS/Denis Balibouse ||||| A U.S. citizen has been detained in North Korea, bringing the total of Americans being held there to three amid increasingly tense relations between the two countries. 
 
 Tony Kim, also known as Kim Sang-Duk, a 58-year-old Korean-American professor and aid worker, had been in North Korea for about a month, was detained on Saturday, the Associated Press reports. 
 
 North Korea has not yet released a reason for Kim’s detention and it has not been reported by media there, CNN reports. 
 
 Here’s what you need to know: 
 
 1. Kim Was Stopped From Boarding a Plane at Pyongyang Airport After Teaching in North Korea for Several Weeks 
 
 Kim Sang-Duk, also known as Tony Kim, 58, was detained at Pyongyang Airport while trying to board a plane to leave the country, CNN reports. He had been teaching for several weeks at the Pyongyang University of Science and Technology, the school said in a statement. 
 
 “We understand that his detention is related to an investigation into matters that are not connected in any way with the work of PUST,” the statement said. “We cannot comment on anything that Mr. Kim may be alleged to have done that is not related to his teaching work and not on the PUST campus. Life on campus and the teaching at PUST is continuing as normal for the spring semester.” 
 
 Kim was teaching accounting at the university, the Los Angeles Times reports. 
 
 The U.S. does not have diplomatic relations with North Korea, so the Swedish embassy is handling consular matters involving U.S. citizens there. 
 
 “We have been informed and can confirm that there has been a detention of a U.S. citizen Saturday morning local,” Martina Aberg, deputy head of mission for the Swedish Embassy in North Korea, told CNN. “He was prevented from getting on the flight out of Pyongyang. We don’t comment further than this.” 
 
 The State Department said Sunday they are working on the case, CNN reports. 
 
 “We are aware of reports that a US citizen was detained in North Korea,” the state department said. “The protection of US citizens is one of the Department’s highest priorities.” 
 
 White House Press Secretary Sean Spicer said at his daily briefing Monday that they are aware of the reports of the detention. 
 
 “The protection of United States citizens is one of our government’s highest priorities,” Spicer said, adding that President Trump would “absolutely” call for Kim to be released. 
 
 “We want to make sure all of our citizens are protected and returned home,” Spicer said. 
 
 He referred all other questions to the State Department. 
 
 2. He Studied & Worked as an Accountant in California Before Becoming a Professor at Yanbian University of Science & Technology 
 
 Tony Kim studied accounting in the United States at the University of California-Riverside and Aurora University, according to his Facebook page. 
 
 Kim worked as an accountant in Los Angeles about 15 years ago, Voice of America Korea reports. 
 
 He had most recently been working as a professor at Yanbian University of Science and Technology, a research university in China’s Jilin province, which borders North Korea, the Los Angeles Times reports. The university has a relationship with the Pyongyang University of Science and Technology in North Korea, where Kim had been working as a guest lecturer. 
 
 Kim was teaching accounting and had been working at Yanbian’s School of Business Administration since it opened, Voice of America reports. Yanbian University has not yet commented. 
 
 PUST was founded in 2010 by evangelical Christians and teaches subjects once banned in North Korea, including capitalism, with students generally coming from the country’s elite, Reuters reports. It is the only privately funded university in the country and is unique for its high amount of foreign faculty, ABC reports. 
 
 3. Kim Was Also Involved in Humanitarian Work, Including Working at Orphanages & Giving Food to Children 
 
 Along with his work as a professor Kim has also been involved in humanitarian work in North Korea, according to Voice of America. 
 
 He would visit orphanage facilities in North Korea, providing food to children there, the news organization reports. He was a regional director in charge of transporting foreign aid materials to several areas in North Korea, including one that suffered flood damage. His humanitarian work has gone on for more than 10 years. According to Korea’s Yonhap news agency, Kim is a devout Christian. 
 
 “Kim is a quiet and sincere person of faith,” a source told Yonhap. “He would not have conducted any anti-North Korea activities.” 
 
 Kim’s Facebook page shows him with his wife and other family members on trips in the United States, including in Hawaii, in 2011 and 2012. He is also a runner, posting photos from road races. 
 
 He posted a photo in 2012 at Pyongyang University of Science and Technology with his soccer team. 
 
 Kim’s wife was with him in North Korea, but was not detained and is still believed to be in the country, CBS News reports. 
 
 4. Experts Say Kim Was Possibly Detained Because of Increasingly Deteriorating Relations Between the U.S. & North Korea 
 
 Experts say that North Korea possibly detained Kim as a negotiating tool as relations with the United States continue to deteriorate. His arrest also comes on the same weekend that a North Korean official threatened in state-run media that they would consider sinking an American aircraft carrier, the Los Angeles Times reports. 
 
 The official said North Korea is ready to sink the U.S.S. Carl Vinson with a “single strike,” and threatened a nuclear attack on Australia if the that country doesn’t stop “blindly and zealously toeing the U.S. line.” 
 
 The Carl Vinson is headed toward the Korean Peninsula and is expected to arrive there later this week. The ship was sent to the area after North Korea conducted a missile test and amid reports that the country could soon conduct its sixth-ever nuclear test, the Times reports. 
 
 North Korea has previously used detained Americans as a way to force the U.S. to begin negotiations, Yonhap reports. 
 
 “This is typical North Korea at a time when there’s so much tension,” former New Mexico Governor Bill Richardson, who has led negotiations with North Korea in the past, told CBS News. “They use…these detainees from the United States as bargaining chips. They always want something in return.” 
 
 Richardson told CBS News the detention might indicate there is a “path forward” as prisoner releases negotiated with the regime have in the past, “led to at least a dialogue with North Korea, and that’s a step forward.” 
 
 5. Two Other Americans – a College Student & a Businessman – Are Serving Hard Labor Sentences of at Least 10 Years in North Korea 
 
 Tony Kim is now one of three American citizens known to be in detention in North Korea, CNN reports. 
 
 Kim Dong Chul, a naturalized U.S. citizen born in South Korea, was arrested in October 2015. Kim, 64, who once lived in Virginia, was residing in China and owned a business in the special economic zone of North Korea, according to CNN. He was convicted of espionage in 2016 and sentenced to 10 years of hard labor. 
 
 Otto Warmbier, a 21-year-old student at the University of Virginia, was detained in January 2016 at Pyongyang airport after visiting North Korea on a tour. He was sentenced to 15 years of hard labor for allegedly removing a political sign from a hotel wall, CNN reports. 
 
 Another Westerner, Canadian Hyeon Soo Lim, 62, is also being held in North Korea. He was sentenced to life in prison with hard labor for crimes against the North Korea regime. Lim is a pastor with the Light Korean Presbyterian Church in Mississauga, Ontario, Canada, and was leading humanitarian efforts in North Korea, providing tens of millions in aid before he was taken into custody in 2015, the Globe and Mail reports. 
 
 There have been U.S. citizens freed from North Korea in recent years, including Merril Newman, an 85-year-old Korean War veteran who was held for two months in October 2013 and Jeffrey Fowle, who spent five months in detention in 2014, according to CNN. Two others, Kenneth Bae and Matthew Todd Miller were released in 2014. There were no known Americans being held in North Korea after their release and until Kim Dong Chul was detained in 2015.
– North Korea on Wednesday confirmed that it detained another American last month, and the reason is the usual one it gives in such cases: It accuses Kim Sang-duk, who also goes by his American name of Tony Kim, of working to "subvert the country," reports Reuters. Kim, believed to be his 50s, was arrested at the airport on April 22 after a month-long stint teaching accounting at the Pyongyang University of Science and Technology, per the New York Times. He teaches the same at a sister school in China. A PUST spokesman says Kim's wife, who was with Kim when he was arrested, was allowed to return to the US. (It's not clear where the Kims reside permanently, though a post at Heavy.com says he worked as an accountant in Los Angeles years ago.) "Invited to Pyongyang University of Science and Technology to teach accounting as a professor, he was intercepted for committing criminal acts of hostility aimed to overturn the DPRK not only in the past but also during his last stay before interception," says the state-run KCNA news agency, using the acronym for the Democratic People's Republic of Korea. Kim reportedly also worked at orphanages in the North. The two other Americans in custody are Otto Warmbier, a 22-year-old student, and Kim Dong Chul, a 62-year-old missionary. Both are serving long prison sentences. (President Trump raised the idea of meeting North Korean leader Kim Jong Un amid tense relations between the countries.)