A North Korean soldier defected across the demilitarized zone that divided the two Koreas on Monday afternoon, in a rare incident at the truce village of Panmunjeom, according to South Korea's Joint Chiefs of Staff.
The soldier was taken to a hospital after being shot by the North Korean side and injured, it said.
Over the decades since the peninsula was divided, dozens of North Korean soldiers have fled to the South through the DMZ, which extends for two kilometers either side of the actual borderline.
South Korean officials detected signs recently that North Korea's military was preparing for winter drills.
South Korea's National Intelligence Service (NIS) confirmed a United States citizen had attempted to enter North Korea via the DMZ, but would not give any further information.
South Korean guards, who were alerted by gunshots, found the North Korean soldier about 55 yards south of Panmunjom, the New York Times reported.
The defector's rank was not immediately clear.
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About 1,000 North Koreans defect to South Korea each year.
Military officials from the North and South have used Panmunjom frequently in the past for talks.
It's the third time this year that a North Korean soldier defected.
South Korea and the United States were also conducting joint military drills in the East Sea utilizing three USA aircraft carriers.
South Korean soldiers ride on an armored vehicle during a South Korea/United States combined training exercise at the U.S. Army's Rodriguez shooting range in Pocheon, northeast of Seoul, Sep.
While in South Korea last week, Trump offered North Korea an opportunity to embrace diplomacy instead of continuing its pursuit of nuclear weapons capable of reaching the mainland U.S.
The drills occurred as President Donald Trump wrapped up a 12-day trip across Asia, in which the North Korean threat was at the top of his agenda.