A U.S. national may be in North Korean custody after crossing the inter-Korean border without authorization, the U.N. Command said on Twitter Tuesday. The person was touring the Joint Security Area — a site at Panmunjeom in the Demilitarized Zone used by North and South Korea for diplomatic engagements and negotiations. The U.S. and North Korea do not currently have formal diplomatic relations. An U.S. travel advisory note urges U.S. nationals not to travel to North Korea "due to the continuing serious risk of arrest and long-term detention." The incident takes place on the same day as a U.S. nuclear submarine visited South Korea for the first time since the 1980s, arriving at the port of Busan, according to the U.S. forces in South Korea.

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Organizations: U.S, Command, Twitter, National, Democratic People's, U.S ., NBC News, White Locations: North, Panmunjeom, South Korea, Democratic People's Republic of Korea, DPRK, U.S, North Korea, An U.S, Busan