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The six-party agreement eased a standoff that began in October 2002, when the U.S. said North Korean officials had admitted having a secret uranium-enrichment program. Washington said that program violated a 1994 agreement for the North’s disarmament, and, a month later, halted oil shipments under that deal.

The North reacted by expelling IAEA monitors, withdrawing from the nuclear Non-Proliferation Treaty and restarting the reactor.

North Korea since then has shut down the reactor occasionally to remove fuel rods and extract plutonium. It is thought to have harvested enough for at least a dozen bombs.

The government set off an underground nuclear test explosion in October, leading to intensified international efforts to negotiate an end to its arms program.

The North was likely to term the shutdown simply a suspension of operations — which could be easily reversed.