Pyongyang, Apr 23 (IANS): North Korean authorities have detained a US citizen of South Korean origin, bringing the number of Americans held by Pyongyang to three, sources in Seoul said on Sunday.

The latest detainee, a man in his late 50s identified only by his surname Kim, was arrested on Friday at the international airport in Pyongyang as he was about to leave the country, the sources told Yonhap news agency.

Kim, a former professor at China's Yanbian University of Science and Technology, was in North Korea to discuss relief activities.

The reason for his arrest was not immediately clear, according to the sources.

The director of the World North Korea Research Centre in Seoul, Ahn Chan-il, told Yonhap that Pyongyang could "use professor Kim as leverage in negotiations" with Washington amid the current escalation in tensions between the two countries.

Two other US citizens currently imprisoned by the North Korean regime are Kim Dong-chul, a sexagenarian of South Korean origin captured near the border with China, and Otto Frederick Warmbier, a student who allegedly tried to steal a propaganda poster while visiting as a tourist, Efe news reports.

Both were sentenced this year to 10 and 15 years of forced labuor respectively.