Shots were fired yesterday 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 neighbors applauded a UN Security Council statement warning the country not to carry out the test, an unprecedented event that some predict could happen as early as today.
South Korea backed the statement and Japan said it would seek punitive measures if Pyongyang does not comply.
On the frontier between North and South Korea, South Korean soldiers fired warning shots after five North Korean soldiers crossed a boundary in the Demilitar-ized Zone separating the countries' forces, South Korean military officials said.
It was unclear whether the North Korean advance -- which happened shortly before noon -- was intended as a provocation, an official at South Korea's Joint Chiefs of Staff said on condition of anonymity, citing official policy. No one was hurt, and the North Koreans retreated.
"It's not clear whether it was intentional or whether it was to catch fish," he said, adding that four North Koreans were unarmed and the fifth carried a rifle.
They advanced about 30m past the Military Demarcation Line separating the two armies before retreating after South Korean forces fired about 40 warning shots, the official said.
The UN Security Council statement, adopted on Friday, urged North Korea to halt the threatened nuclear test and return immediately to talks on scrapping its nuclear weapons program, warning of unspecified consequences.
South Korea's Foreign Ministry said it supported the appeal and urged its isolated neighbor to return to long-stalled, six- nation talks on ending its nuclear weapons program.
"North Korea must clearly recognize that a nuclear test would not help the North itself in any way," a ministry statement said.
"North Korea should be held responsible for any consequences that could be caused by a test," it added.
South Korea's nuclear envoy said he would visit Beijing tomorrow for two days of talks about the nuclear test, while Japan's Foreign Ministry said such a test posed "a grave threat to the peace and security of northeast Asia and the world."
"If North Korea conducts a nuclear weapons test despite the concerns expressed by international society, the Security Council must adopt a resolution outlining severely punitive meas-ures," the ministry said.
Japan plans to step up economic sanctions against North Korea, tighten trade restrictions and freeze additional North Korea-linked bank accounts if a test were carried out, Japan's Nihon Keizai Shimbun reported.
The council statement adopted unanimously on Friday expressed "deep concern" over North Korea's announcement on Tuesday that it planned a test in a move that would confirm its boasts that it is a nuclear power.
The warning was read at a formal meeting by the Council president, Ambassador Kenzo Oshima of Japan, who indicated that North Korea could face sanctions or possible military action if it detonates a nuclear device.