The North Korean government announced Saturday it has detained a South Korean student who attends New York University for entering the country illegally. The student, Joo Won Moon, was arrested on April 22 after crossing the Yalu River from China without authorization, according to the state-controlled Korean Central News Agency.

Joo, 21, is said to live in New Jersey and hold permanent resident status in the United States, according to the New York Times. The South Korean government did not immediately confirm the Korean Central News Agency's report, though Pyongyang has captured and detained a number of Americans, missionaries and aid workers in recent years, calling them spies. Americans Kenneth Bae, a missionary, and Matthew Todd Miller were released from North Korea on Nov. 8 last year, when U.S. Director of National Intelligence James Clapper made a secret trip to the isolated nation and negotiated their freedom.

Little is known about Joo's arrest, though he was taken into custody after allegedly departing the Chinese town of Dandong and traveling across the waterway that forms part of North Korea's border with China.

It's especially dangerous for travelers from South Korea to cross the boundary into North Korea. Two South Korean men were taken into custody in March and accused of espionage, including charges that they illegally collected military secrets and spread political propaganda on behalf of South Korea's spy agency. South Korea has consistently refuted such charges and called for the immediate release of its prisoners. The two countries have existed in a state of war since the Korean War of 1950-1953 ended in a truce rather than a peace treaty.