A North Korean soldier has defected to the South across the two countries' heavily armed border, South Korean officials have said.
The soldier said he shot dead his platoon and squad chiefs while on guard duty before crossing over on Saturday.
The BBC says defections across the land border are rare, with the last soldier fleeing in October 2008.
More than 24,000 North Korean civilians have gone to the South in the last 60 years, mostly via China.
The Defence Ministry official said the soldier was in protective custody and was still being questioned.
There has been no confirmation of the North Korean casualties and no unusual activity observed on the North Korean side of the border.
The two countries are still technically at war after the 1950-53 conflict, which ended in a ceasefire not a peace treaty.