Shots were fired on Saturday along the heavily armed no man's land separating the divided Koreas as regional tensions mounted in anticipation of communist North Korea carrying out its first atomic bomb test.
North Korea's neighbours applauded a UN Security Council statement, made on Friday, warning the country not to carry out the test, an unprecedented event that some predict could happen as early as Sunday, the anniversary of North Korean leader Kim Jong II's appointment as head of the Korean Workers' Party in 1997.
South Korea backed the statement, and Japan said it would seek punitive measures if Pyongyang does not comply. A North Korea expert in China, the North's closest ally, said only the lifting of US economic sanctions against Pyongyang could dissuade the country from testing.
A Chinese source briefed by Pyongyang told Reuters that a device would be detonated about 2,000 metres inside a mine near the border with China in the north of the country.
Kim had issued instructions that the test should "not excessively rock" Mount Paektu, a nearby peak that many Koreans consider sacred.