The warning, delivered in a statement carried by the communist regime's official Korean Central News Agency, came hours after a South Korean newspaper reported that a U.S. spy satellite detected signs the North had positioned about 10 missiles on an island near the disputed sea border after test-firing two short-range missiles on Tuesday. The Chosun Ilbo report cited an unidentified South Korean government official.
Later Thursday, North Korea told the International Atomic Energy Agency in Vienna that it was banning inspectors from its main nuclear complex in Yongbyon and stopping its program to dismantle the site, the agency said.
It was the clearest indication to date that the North plans to pull out of an international deal to end its nuclear program, said a senior diplomat linked to the IAEA who requested anonymity because he was not authorized to comment to the media.
In Washington, Secretary of State Condoleezza Rice, responding to reporters' questions about Thursday's developments, said the Bush administration was "reviewing the situation."
Pyongyang had already barred U.N. weapons personnel from a plutonium reprocessing facility last month, one of three main installations at Yongbyon, as it took steps to restart its weapons-producing atomic program in violation of an international disarmament-for-aid accord.
The North's latest moves come at a time of increasing concern about security on the Korean peninsula.
The two Koreas remain technically at war since the Korean War ended on June 25, 1953, with an armistice, not a peace treaty. North Korea does not recognize a sea boundary unilaterally drawn by the U.N. at the end of the war, and the waters off Korea's west coast remain in dispute.
In its warning Thursday, North Korea said the recurring maritime dispute was "so dangerous that a third West Sea skirmish and a second June 25 war may break out at any moment."
South Korea's Defense Ministry said the country has never violated the sea border.
On Tuesday, North Korea reportedly fired two short-range missiles off the west coast. South Korean intelligence officials believe the North is planning to fire more than five additional missiles in coming days, the Chosun Ilbo report said, noting that the North had banned ships from the waters until next Wednesday.
South Korea's Defense Ministry, the National Intelligence Service and the U.S. military command in Seoul said they could not confirm the reports.
North Korea routinely test fires short-range missiles as part of its military training, but rarely such a large number at once. It conducted an underground nuclear test two years ago and in 2006 fired seven missiles off the country's eastern coast.
In 2007, the North agreed to dismantle its nuclear program in exchange for energy aid and other concessions. But it abruptly stopped disabling the Yongbyon facility in mid-August, over objections to U.S. demands for verification of its atomic program. Washington had made verification a condition for removing North Korea from a list of nations that sponsor terrorism.
