SEOUL, South Korea -- North Korea's government said Tuesday it has begun to freeze its nuclear program in compliance with the accord it signed with the United States.


But North Korea also condemned U.S. and South Korean troops for beginning the first major field exercise this year and said it could bring the Korean Peninsula back to the brink of war.


In the agreement that officials from Washington and Pyongyang signed in Geneva on Oct. 21, the North agreed to freeze, then dismantle, a nuclear system suspected of building atomic weapons.


In return for modern technology, aid and diplomatic relations with the United States, North Korea also promised to eventually open its nuclear installations to full international inspections.


North Korea's Foreign Ministry told the official Korea Central News Agency on Tuesday that it has stopped building two nuclear reactors, one of 50 megawatts and one of 200 megawatts.


During 17 months of negotiations with the North, U.S. officials warned that if the plants were finished, they could produce enough plutonium for several nuclear bombs a year.


The Foreign Ministry also said it has shut down a 5-megawatt reactor and decided not to reload it with new fuel rods.


In May, the North removed 8,000 spent fuel rods from the reactor and threatened to produce plutonium from them. That prompted the United States to threaten to end the negotiations in Geneva.


Because hard-line Communist North Korea is closed to the outside world, and nuclear inspectors have not re-entered the country yet, there was no way to confirm North Korea's statement.


In fact, earlier Tuesday, the North had said the U.S.-South Korean military exercise could prevent it from complying with the accord.


When U.S. and North Korean officials signed the nuclear agreement last month, South Korea made a political gesture to the North by canceling this year's annual Team Spirit exercise, which rehearses the American and South Korean defense of the peninsula.


However, South Korea and the United States decided to go ahead with their annual Foal Eagle exercise, which involves the majority of the South's 650,000 soldiers and 4 million reservists, and about 25,000 of the 36,000 U.S. soldiers stationed in South Korea.


"The exercises are a display of (South Korea's) reckless war frenzy to throw a wet blanket over the framework agreement," the first Korea Central News Agency communication said Tuesday.


It also said the maneuvers would "hinder its implementation" and "further aggravate the North-South relations and drive the situation ... back to the brink of war."


Tensions have been high during the past year because of suspicions that North Korea is building nuclear weapons.


North Korea stations 1.2 million soldiers near the demilitarized zone, which is only 55 kilometers north of Seoul.


The two Koreas are still technically at war, never having signed a peace treaty to officially end the 1950-53 Korean War.


During Foal Eagle, the military will summon the reservists, see how long it takes them to report for duty, and test their equipment, said Jim Coles, the U.S. military command spokesman.


Mostly south of Seoul, U.S. and South Korean soldiers, their commanders and their communication systems will be tested on their ability to stop rear-area attacks, he said.


People living near the exercises will be kept informed about them in several ways, including leaflet drops, Coles said.


"North Korea often complains about these exercises, but they are purely defensive, not provocative," he said in an interview.


Meanwhile, the North appears to have ignored a U.S. request to begin withdrawing troops from the tense Korean border.