A North Korean soldier defected to the South on Saturday through the heavily militarised border, telling Seoul military personnel that he had shot dead two officers, the Joint Chiefs of Staff said.
"Our soldiers standing guard at an outpost heard shots... and spotted a North Korean soldier coming over to the South. They led him to safety," a spokesman for the Joint Chiefs of Staff told reporters.
"According to the defector, he shot dead his platoon leader and a company commander before crossing the border," the spokesman said, adding the soldier was in protective custody.
South Korean soldiers in the area, on the western part of the inter-Korean border, were put on alert after the incident around 12:10 pm (0310 GMT).
No independent confirmation of any North Korean casualties was immediately available.