The Yonhap news agency cited a spokesman for South Korean Joint Chiefs of Staff as saying the firefight took place near Inje, 165 (100 miles) kilometers northeast of Seoul, on the eastern portion of the buffer zone that has separated the two Koreas for over 50 years.
The spokesman said North Korean soldiers started the shootout and South Korean soldiers immediately fired back at least 10 rounds. No casualties have been reported from either side so far.
"Our military fired a few warning shots and demanded through a loudspeaker that North Koreans stop firing and apologize but no reaction from the North has followed," the agency quoted the official as saying.
The spokesman said it was too early to say whether the North opened fire deliberately or by accident, but another South Korean military source suggested that Pyongyang could have orchestrated the incident on the eastern stretch of the 248-kilometer (155 mile) Demilitarized Zone to increase tensions at the upcoming talks on North Korea's disarmament.
The talks, involving the two Koreas, Russia, China, Japan and the United States, are part of an international effort to persuade the reclusive Communist regime to abandon its nuclear weapons program in exchange for humanitarian aid.
The four-kilometer (2.5 miles) wide and heavily fortified Demilitarized Zone has divided the Korean Peninsula since the 1950-1953 Korean War.
The last incident in the area occurred on July 31, 2006, when, according to a South Korean claim, North Korean soldiers fired two shots at a South Korean guard post in the eastern part of the buffer zone.
