South Korea's joint chiefs of staff charged North Korean forces with "launching the first shots" at a South Korean guard post just below the demilitarized zone (DMZ) that has divided the Korean peninsula since the end of the Korean War in July 1953.
A South Korean defense official said South Korean soldiers had fired three shots back across the DMZ "under the rules of engagement."
The shootout was the first such flare-up on land in two years, but North and South Korean warships clashed in the west or Yellow Sea on several occasions before the South Korean Cheonan warship was torpedoed in March.
There was "no damage from the North Korean shots," said the official in a statement to the South Korean media, and it was not even certain if North Korean soldiers were deliberately aiming at the guard post.
He said the United Nations Command, a US-led organization that dates from the Korean War, in overall authority over South Korean troops as well as the 27,500 American troops still in Korea, would investigate "to determine whether North Korea had violated terms of the armistice."
Tensions run high
Tensions are always high in the isolated region, the scene of some of the bloodiest fighting in the Korean War. South Korean officials were concerned that North Korea might have chosen it as a likely place for a show of force after South Korea refused to engage in another round of inter-Korean military talks.
South Korean officials have described such talks as a waste of time in view of North Korea's refusal to acknowledge responsibility for torpedoing the Cheonan navy corvette in March in which 46 sailors died.
North Korea has yet to comment on the shootout but called the rejection of military talks "an act of treachery," according to the North's Korean Central News Agency. South Korean authorities, said KCNA, should be aware of the "catastrophic impact" of the rejection on North-South relations.
South Korean troops along the 160-mile-long DMZ were on alert amid extra precautions in the run-up to the G20 summit that South Korea is hosting here on Nov. 11 and 12. With President Obama and leaders from 18 other countries and the European Union converging here, officials and politicians have been speculating about whether North Korea might time an incident for the event.
Tensions have eased of late, however, with 430 elderly South Koreans from 97 families due to meet long-lost loved ones this weekend in a long-delayed reunion of families divided by the Korean War.
The reunion, the first in more than a year, is to be in North Korea's Mount Kumkang tourist zone by the east coast about 30 miles from the scene of the shooting. South Korea's unification ministry said the reunion would go on as scheduled despite the shootout.
Moreover, South Korea this week shipped 5,000 tons of rice as emergency food aid to the North – the first aid from the South Korean government to North Korea since the conservative President Lee Myung-bak was inaugurated in February 2008.
North Korea has demanded 500,000 tons, the amount shipped annually during the ten years before Mr. Lee took office, but he has said the North must first act to get rid of its program for building nuclear weapons.