Originally posted by the Voice of America. Voice of America content is produced by the Voice of America, a United States federal government-sponsored entity, and is in the public domain. US Citizen in North Korean Custody After Crossing North at Border Town by Eunice Kim SEOUL, SOUTH KOREA -- A U.S. national is believed to be in North Korean custody after illegally crossing the border dividing the two Koreas at the Joint Security Area, or JSA, on Tuesday. The United Nations Command, a multinational military force stationed at the border village to maintain the pause to the Korean War, said it is working with North Korea's military to "resolve the incident," confirming that the man was on a JSA orientation tour. The man in question suddenly crossed north of the military demarcation line, the official border, at around 3:27 p.m. local time on Tuesday afternoon, according to South Korean daily The Chosun Ilbo, citing unnamed sources. No fire appeared to have been exchanged at the high-tension border town, where soldiers from the two Koreas stand guard around the clock, facing each other. According to reliable sources in the South Korean military, the American who crossed the border is a U.S. soldier, a private, stationed with United States Forces Korea. The incident occurred as South Korea's military remains on high alert for possible provocations from North Korea after a U.S. nuclear ballistic missile submarine arrived in port in the southern city of Busan on the same day. Arrival of the USS Kentucky, capable of launching Trident II ballistic missiles with a range of 12,000 kilometers, is a highly symbolic move that Washington will stand with South Korea in the event of a North Korean nuclear attack. It is the first visit of a U.S. nuclear submarine in decades, said the White House Indo-Pacific coordinator, Kurt Campbell, during a press conference in Seoul Tuesday. Campbell is leading a 30-person delegation to officially launch the Nuclear Consultative Group, or NCG, with Seoul. South Korea says the initiative will strengthen their alliance to one that is nuclear based. It is the realization of a commitment made by U.S. President Joe Biden and South Korean President Yoon Suk Yeol in April, as outlined in the Washington Declaration. A joint statement following the inaugural meeting of the NCG noted that any North Korean nuclear attack against the United States or its allies would "result in the end of that regime," and that a nuclear attack against South Korea would "be met with a swift, overwhelming and decisive response." VOA's Korean service contributed to this report.