A North Korean soldier walked across the heavily armed border between North and South Korea in a bid to defect to the South, an official at the South Korean Defence Ministry said on Monday.
The official did not immediately have further details.
Yonhap news agency said South Korea's military had secured custody of the soldier near the border in the peninsula's central region.
While there are more than a thousand defections from North Korea to South Korea every year, most defectors cross the border into China and it is rare for a North Korean to defect by crossing the Demilitarised Zone (DMZ).
Yonhap said the defection is the first across the DMZ since October 2012.
Citing military sources, the news agency said Pyongyang appears recently to have stepped up efforts to prevent defections across the DMZ by beefing up patrols along the border and checking to see if border markers are properly set up. There are 1,292 wood or concrete markers every 200 to 300 meters along the tensely-guarded border, Yonhap said.