North Korea Threatens War Against U.S.

North Korea stoked regional tensions Wednesday, threatening more nuclear tests and saying additional sanctions imposed on it would be considered an act of war, as nervous neighbors raced to bolster defenses and punish Pyongyang.

South Korea said it was making sure its troops were prepared for atomic warfare, and Japan imposed new economic sanctions to hit the economic lifeline of the communist nation's 1 million-member military, the world's fifth-largest.

North Korea, in its first formal statement since Monday's claimed atomic bomb test, hailed the blast as a success and said attempts by the outside world to penalize North Korea with sanctions would be considered an act of war.

Further pressure will be countered with physical retaliation, the North's Foreign Ministry warned in a statement carried by the official Korean Central News Agency.

"If the U.S. keeps pestering us and increases pressure, we will regard it as a declaration of war and will take a series of physical corresponding measures," the statement, said without specifying what those measures could be.

Secretary of State Condoleezza Rice said the United States would not attack North Korea, rejecting a suggestion that Pyongyang may feel it needs nuclear weapons to stave off an Iraq-style U.S. invasion.