The tension between the North Korea and the United States just rose even further when the elusive state detained their third American prisoner. Tony Kim, who also go by Kim Sang-Duk, was arrested as he was about to leave Pyongyang, reports say.

Currently, since the diplomatic relationship between the two countries is in hot waters and as there's no US Embassy in the North, the Swedish Embassy in Pyongyang currently handles all consular matters involving American nationals there, according to NBC News.

Kim, a 58-year-old academic, came to the North to teach accounting at the Pyongyang University of Science and Technology for about a month. As he was about to board the plane back to the US at the Pyongyang International Airport, authorities immediately made his arrest, and he hasn't been seen since.

Official reasons for Kim's arrest haven't been announced yet, Chicago Tribune reports. But according to South Korea's Yonhap news agency, "Kim is a former professor at the Yanbian University of Science and Technology, a research university in China's Jilin province, which borders North Korea."

The US State Department is already aware of Kim's arrest and has already made a statement last Sunday. They have also been working closely with the Swedish Embassy in Pyongyang. Due to the sensitivity of the issue, they declined more information about the incident.

North Korea currently holds two other American citizens in prison. It was only last year when Otto Warmbier, a then 21-year-old student from the University of Virginia, made headlines when the North sentenced him to 15 years of hard labor in prison after it was discovered that he tried to steal a propaganda banner from a hotel during his five-day visit to the country.

The next month after Warmbier's arrest, Kim Dong Chul, a 62-year-old South Korean with a U.S. citizenship, got arrested as well and was sentenced to 10 years of hard labor for espionage. A pastor from Canada is currently being detained in the country as well since early 2015.