But the North's Foreign Ministry also said it was as ready for dialogue as for war. The comment indicated it has not abandoned a reconciliation process that stalled this year after stern pronouncements from President Bush infuriated North Korean leaders.
South Korean defense officials, accustomed to fiery rhetoric from the North, said they would go ahead with the weeklong war games, which start Friday.
"It's common North Korean propaganda. We are not too concerned about it," a spokesman at South Korea's office of Joint Chiefs of Staffs said on condition of anonymity.
The annual exercise involves 10,000 troops who conduct mostly computer simulation tests. Some of the 37,000 U.S. soldiers stationed in the South, as well as American troops from bases in Japan, Hawaii and the U.S. mainland, will participate.
South Korea and the United States describe joint military training as defensive, but North Korea condemns the maneuvers as rehearsals for invasion.
The North Korean statement was one of countless condemnations in the tense decades since the 1950-53 Korean War. But it was unusual because the North had largely refrained from criticizing or threatening the South since their summit agreement last year.
"If the South Korean authorities defiantly take part in the projected war exercise in pursuance of the U.S. war moves against (North Korea), their behavior cannot be construed otherwise than a downright betrayal to the North-South joint declaration," the Foreign Ministry said in a statement carried by KCNA, the North's foreign news outlet.
However, the statement also said: "We are prepared both for dialogue and for war."
Seo Joo-seok, an analyst at the state-funded Korea Institute for Defense Analysis, said the North Korean announcement was "a signal that further delays in inter-Korean dialogue can be expected."
The mood in the South was euphoric last year after President Kim Dae-jung and North Korean leader Kim Jong Il met in Pyongyang in June. They agreed to try to shed the hostility that has characterized inter-Korean ties since the peninsula was divided at the end of World War II.
A flurry of official contacts ensued. But the exchanges have dried up in recent weeks since Mr. Bush said he had no plans to engage Pyongyang before completion of a review of the North Korea policy he inherited from former President Clinton.
Tough talk from U.S. officials in Paris last week, Secretary of State Colin Powell bluntly referred to the North as a "totalitarian regime" also angered the North Koreans.
Air raid sirens blared Monday over the South Korean capital, Seoul, in a civil defense exercise held several times a year. Police stopped traffic in some major intersections for 15 minutes, and employees practced evacuations at some state offices.
Impoverished North Korea has more than a million soldiers but lacks modern equipment and vital resources such as fuel. U.S. and South Korean commanders, however, fear Pyongyang could devastate Seoul, just 43 miles south of the Demilitarized Zone, with artillery barrages in the early hours of a conflict.
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