South Korea's defence chief has had to apologise after troops failed to spot a North Korean soldier defecting across their heavily guarded border.
No one spotted the soldier - even though he scaled barbed wire fences on the South Korean side of the border - until he knocked on the door of front-line South Korean barracks.
The incident raised serious questions about South Korea's military surveillance capabilities.
Defence minister Kim Kwan-jin said he "deeply" apologises for causing public concern over the defection.
"There were an obvious failure in security operations and faults in situation-reporting systems," he said.
A total of 14 officers, including five at the general level, will be investigated for possible punishment over the incident.
The defence ministry said border security will be strengthened by deploying more guards and modern surveillance equipment and installing more fences.
The Korean Peninsula has remained divided along a 2.5-mile-wide Demilitarised Zone since the Korean War ended with an armistice, not a peace treaty, in 1953. It is guarded by hundreds of thousands of combat-ready troops on both sides and is strewn with mines and laced with barbed wire.
About 24,000 North Koreans have defected to South Korea since the end of the Korean War, but defections across the land border rare with the vast majority of defectors fleeing through China and South-East Asian nations for the South.
Defections by soldiers are unusual as well, although another North Korean soldier defected to South Korea via the land border after killing two of his superiors earlier this month.