Seoul, South Korea ? North Korea threatened today to abandon the 1953 armistice that ended the Korean War, accusing the United States of plotting a naval blockade as a prelude to an attack over the communist state’s nuclear program.

“The situation on the Korean Peninsula is getting extremely tense” because the United States is planning to send reinforcements in a standoff over the North’s nuclear activities, said a spokesman for the North Korean army.

North Korea “will be left with no option but to take a decisive step to abandon its commitment to implement the Armistice Agreement … and free itself from the binding force of all its provisions,” said the official.

The 1950-53 Korean War ended with the armistice, not a peace treaty, leaving the countries technically in a state of war. A North Korean withdrawal from the armistice would greatly increase tensions and uncertainty along the world’s most heavily armed border.

State Department officials in Washington had no immediate reaction to the North’s threat. A U.S. official, speaking on condition of anonymity, noted the Bush administration had said in the past it would not respond to threats or blackmail.

The announcement, reported by the North’s state-run KCNA news agency, is the latest move in the standoff over Pyongyang’s threat to restart its nuclear programs in violation of international treaties.

Washington and its allies are pressuring North Korea to abandon its nuclear ambitions.

The North, however, has insisted on direct talks first with the United States, from which it wants a nonaggression treaty.

North Korea has previously threatened several times to pull out of the armistice in an attempt to increase tensions with the United States and force Washington to start negotiations with the Stalinist regime in Pyongyang. It has never followed through on the threat.