A man identified as a South Korean student at New York University is being detained in North Korea, according to the South’s unification ministry, one day after the North’s state news agency said it had arrested and charged him with illegally entering the reclusive country. New Jersey resident Won Moon Joo, 21, was arrested April 22 after apparently attempting to cross a river that serves as part of the border between China and North Korea, the Korean Central News Agency said.