SEOUL — North Korea has detained a US citizen, the Swedish Embassy in Pyongyang and a university chancellor said Sunday, raising the number of Americans thought to be held by the secretive nation to three.

The arrest, if confirmed, would further complicate Washington’s relations with the country at a particularly tense moment.

The man, Tony Kim, who also goes by his Korean name, Kim Sang-duk, was detained on Saturday, Park Chan-mo, the chancellor of Pyongyang University of Science and Technology, told the Associated Press.

Park said Kim had taught accounting at the university for about a month and had taught at Yanbian University of Science and Technology in China before coming to Pyongyang. He said Kim had been detained by officials at Sunan International Airport in Pyongyang as he was trying to leave North Korea.

Officials had no immediate information on Kim’s hometown.

South Korea’s Yonhap News Agency, citing unnamed sources, earlier said that a Korean-American man identified only by his last name, Kim, had been arrested at the airport. It said the man, who is in his late 50s and is a former professor at Yanbian University, has been involved in aid and relief programs to North Korea.

The Swedish Embassy in Pyongyang, the capital, said it was aware that the North had recently detained a Korean-American citizen, the Associated Press reported. The United States does not have formal diplomatic ties with North Korea, and the embassy looks after consular affairs in the North on behalf of Washington.

The South Korean government, including its Unification Ministry and National Intelligence Service, said it could not confirm the report.

North Korea has been accused of holding Americans on what many see as dubious charges in order to use them as diplomatic leverage. At least two other Americans are known to be held in the country.

Relations with Washington have reached a pitch recently, as North Korea has tested missiles and the United States has threatened to send warships to the region.

North Korea said Sunday it was ready to sink a US aircraft carrier to demonstrate its military might, as two Japanese navy ships joined a US carrier group for exercises in the western Pacific, Reuters reported.

“Our revolutionary forces are combat-ready to sink a US nuclear-powered aircraft carrier with a single strike,’’ Rodong Sinmun, the newspaper of the North’s ruling Workers’ Party, said in a commentary.

The carrier USS Carl Vinson, which is heading toward the Korean Peninsula, began joint exercises Sunday with the Japanese naval ships in the Philippine Sea.

The Vinson, along with a US guided-missile cruiser and guided-missile destroyer, are continuing their journey north in the western Pacific Ocean, the Navy said. The Vinson had canceled a scheduled visit to Australia to divert toward North Korea in a show of force, though it still conducted a curtailed training exercise with Australia before doing so.

Two Japan Maritime Self-Defense Force destroyers left Sasebo port in southern Japan on Friday to join the Vinson strike group.

The Vinson group has conducted three previous bilateral exercises with the Japanese navy since leaving San Diego on Jan. 5 for a western Pacific deployment. The most recent one was in March.

The Navy called the latest exercise ‘‘routine’’ and said it is designed to improve combined maritime response and defense capabilities, as well as joint maneuvering proficiency.

Kim had been teaching a class in international finance and management at the Pyongyang University of Science and Technology, a sister institution of Yanbian, for a month and was leaving the country with his wife when he was arrested, the website NK News reported.

North Korea has taken several Americans hostage in recent years and used them as bargaining chips in negotiations with the United States.

Last year, North Korea sentenced a US college student, Otto F. Warmbier, to 15 years of hard labor after accusing him of trying to steal a political banner from his hotel in Pyongyang. It later sentenced another American, Kim Dong-chul, to 10 years’ hard labor on charges of spying and other offenses.

In 2014, a US citizen, Jeffrey E. Fowle, was arrested and accused of leaving a Bible in a hotel. He was freed later that year.

Kenneth Bae, a Korean-American missionary sentenced to 15 years’ hard labor after he was charged with trying to establish a secret proselytizing network, was freed in 2014, after the US government sent the director of national intelligence at the time, James R. Clapper Jr., to North Korea.

Americans are not the only foreigners being held in the North. In 2015, a South Korea-born Canadian pastor was sentenced there to hard labor for life on charges of plotting to overthrow the North Korean leadership. The North has also arrested at least four South Koreans in recent years.

Previous American detainees have been released after a few months, following visits from high-profile Americans, including former presidents Bill Clinton and Jimmy Carter.