A North Korean soldier defected to South Korea Saturday across the heavily armed border, claiming that he fled after shooting two superiors to death, the Joint Chiefs of Staff said.

The solider crossed the western sector of the Demilitarized Zone separating the two Koreas at 12:06 p.m. and arrived at a South Korean guard post four minutes later, the JCS said in a statement.

South Korean border guards heard six gunshots at the time before finding the North Korean soldier running across the border. The guards used a loudspeaker to confirm his desire to defect before escorting him into custody, JSC officials said.

The soldier, whose exact rank was not disclosed, was not armed when he surrendered, they said.

The defector told South Korean investigators that he fled after shooting his platoon and squad leaders to death while on guard duty, the JCS said, adding that he was being questioned by a joint team of investigators from related agencies.

North Korean soldiers were seen moving two bodies at a guard post, the officials said.

The area is where South Koreans travel through to visit an inter-Korean industrial complex in the North Korean border city of Kaesong, where more than 50,000 North Koreans work at about 120 South Korean factories.

Guard posts of the two sides in the area are only 500 meters apart.

Despite the incident, about 300 South Korean workers returned home from the Kaesong Industrial Complex between 2 p.m. and 2:30 p.m. as previously scheduled, Seoul officials said. Still, two South Koreans canceled their previously arranged trip to the industrial complex apparently out of security concerns, they said.

South Korea's military has strengthened vigilance in the area, but the North's military has not shown any signs of unusual movement, the JCS said.

Defection via the DMZ is rare as the border is tightly sealed and heavily armed. It is the first overland defection since a North Korean soldier crossed the eastern section of the border in March 2010.

South and North Korea are still technically at war since the 1950-53 Korean War ended in a truce, not a peace treaty. (Yonhap)