A Korean-American former college professor was arrested Friday in North Korea, making him the third U.S. citizen held by Pyongyang, Yonhap reported Sunday citing unnamed sources.

The man, identified only by his surname, Kim, was arrested at Pyongyang International Airport while on his way out of the country, Yonhap said.

Kim was said to be in his late 50s and a former professor at Yanbian University of Science and Technology in Jilin Province, China.

Yonhap said Kim reportedly had been in North Korea for about a month to "discuss relief activities," and it was not known why he had been arrested.

In March 2016, college student Otto Warmbier from Cincinnati, Ohio, was sentenced to 15 years hard labor for allegedly attempting to steal a political banner from a Pyongyang hotel while in North Korea on a five-day visit.

And the following month Kim Dong Chul, a South Korean-born naturalized American citizen, was sentenced to 10 years hard labor for spying. Kim Dong Chul, a onetime resident of Fairfax, Virginia, reportedly had been living in China with his wife and owned a business in a special economic zone within North Korea.

Yonhap said, "The widespread view has been that Pyongyang uses the detentions as bargaining chips in its negotiations with Washington."

==Kyodo