Soldiers from North and South Korea have exchanged machine gun fire as tensions rise amid efforts to resolve a crisis over Pyongyang's nuclear weapons programme.
South Korea says one its guard posts was fired upon
Reports of the incident in the demilitarised zone north of Seoul came as the United States expressed optimism over China's attempts to defuse the dispute.
US Secretary of State Colin Powell - speaking after a phone conversation with Chinese Foreign Minister Li Zhaoxing - said he expected to see diplomatic movement to end the deadlock soon.
The BBC Seoul correspondent, Charles Scanlon, says North Korea has used border provocations in the past to reinforce its diplomacy. North Korea has a tradition of raising the stakes in a negotiation before settling for a deal.
Chinese envoys have been holding talks with North Korean leader Kim Jong-il amid mounting concerns over the country's nuclear programme.
The border incident happened at 0610 local time on Thursday (2110 GMT on Wednesday), and was over quickly.
The South Korean military said the North Koreans fired four rounds from a machine gun at one of its posts along the DMZ.
It said South Korean troops broadcast a warning through loudspeakers and then returned fire with 17 shots. There were no reported casualties.
Our correspondent says exchanges of gunfire between the vast armies dug in on either side of the line have been relatively rare in recent years, although six South Korean sailors and an unconfirmed number from the North were killed in a naval clash last year.
The incident happened shortly after Mr Powell said he was upbeat on finding a solution to the row over the North's nuclear ambitions.
"The diplomatic track is alive and well and I expect to see some developments along that track in the very near future," he said.
Unnamed State Department officials said the US had heard, via China, that the North Koreans were willing to resume multilateral talks similar to those held in Beijing earlier this year.
Chinese Vice Foreign Minister Dai Bingguo, who has recently held talks with the North Korean administration, is due to travel to Washington for talks later this week.
The Bush administration has been insisting on a multilateral approach to the North Korea weapons dispute, which would involve its regional allies South Korea and Japan.
The US does not want to be painted into a diplomatic corner, nor to prolong Pyongyang's political leadership if it can help it, says the BBC's David Bamford in Washington.
Neither side has signed up publicly to whatever the Chinese compromise might be - possibly two-way talks within a wider regional forum - but Mr Powell is sounding increasingly positive that a middle way might be found, our correspondent says.