SEOUL, South Korea — A North Korean soldier killed two of his officers Saturday and defected to South Korea across the countries' heavily armed border, officials said.

The soldier shot his platoon and company commanders before crossing the Demilitarized Zone at around noon, a Defense Ministry official said, citing the soldier's statement after he was taken into custody by South Korean border guards.

The official declined to be named because questioning by authorities was still under way.

No unusual military movement was detected from the North Korean side of the border after the crossing, a South Korean Joint Chiefs of Staff official said. He also declining to be named, citing office rules.

Defections across the land border are rare. Last year, a North Korean civilian defected to the South across the land border. The last known defection across the border by a North Korean soldier occurred in October 2008. A North Korean officer also defected in a similar fashion in April that year.

The vast majority of North Koreans fleeing their homeland travel through China and Southeast Asia before arriving in the South.

More than 24,000 North Koreans have arrived in the South since the 1950-53 Korean War ended in a cease-fire, not a peace treaty.