John Bacon

USA TODAY

A U.S. citizen has been arrested in North Korea, raising to three the number of Americans now detained by Kim Jong Un's regime and adding to rising tensions between Washington and Pyongyang.

South Korea's Yonhap news agency reported that a former Korean-American professor was arrested at Pyongyang International Airport as he was attempting to leave the country.

Yonhap described Kim as a former professor at the Yanbian University of Science and Technology in Yanji, Jilin, China. Yonhap said Kim, in his late 50s, had been involved in aid programs in North Korea. The reason for his arrest was not immediately available.

The U.S. State Department said it was aware of reports that an American had been detained but declined to reveal details.

"The protection of U.S. citizens is one of the Department's highest priorities," the State Department said in a statement. "In cases where U.S. citizens are reported to be detained in North Korea, we work with the Swedish Embassy, which serves as the United States' Protecting Power in North Korea."

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The Swedish embassy confirmed to multiple news organizations that an arrest took place Saturday but did not immediately respond to a request for more information from USA TODAY.

Park Chan-mo, the chancellor of the Pyongyang University of Science and Technology, identified the man to the Associated Press as Tony Kim. Park told AP Kim had come from the Chinese school and taught accounting in Pyongyang for about a month.

Relations between the U.S. and North Korea have grown more strained in recent months, with Pyongyang continuing to conduct nuclear and ballistic missile testing in defiance of international bans. North Korea's leader has been equally outraged by massive joint military exercises conducted by the U.S. and South Korea.

Pyongyang said Sunday it was poised to destroy the USS Carl Vinson if provoked when the aircraft carrier and its armada arrive at the Korean Peninsula. The ship began exercises Sunday with Japan, the Navy said. Last week, Vice President Pence visited South Korea and Japan, warning that the U.S. response to any use of weapons by North Korea would be "overwhelming and effective."

“The United States of America will always seek peace but under President Trump, the shield stands guard and the sword stands ready," Pence said.

On Thursday, the U.N. Security Council condemned North Korea over its latest missile earlier this month. The statement included a call for dialogue and significantly was supported by China, North Korea’s closest ally.

Ahn Chan-il, director of the World North Korea Research Center in Seoul, told Yonhap that Pyongyang "seems to be intending to use professor Kim as leverage in negotiations" with the U.S.

Other Americans being held in North Korea include Ohio native Otto Warmbier, a University of Virginia student who was arrested in January 2016 while he was on a tour of North Korea, and Kim Dong Chul, who was arrested in October 2015 while in North Korea on business.

Warmbier was accused of committing a "hostile act" for allegedly trying to steal a political banner and was sentenced in March 2016 to 15 years hard labor. Kim was accused of stealing military secrets and is serving a 10-year sentence.

Warmbier's parents expressed frustration Friday at efforts to win freedom for their son. Fred Warmbier told Fox News that neither the Obama administration nor the Trump administration had given them reason to hope their son would come home soon. He said no one in the Trump administration has called them, and their main contact with the State Department was a low-level employee.

“President Trump, I ask you, bring my son home,” Warmbier said.

Contributing: Deirdre Shesgreen