North Korea ordered the removal of the UN seals and surveillance equipment, which the International Atomic Energy Agency did.
The IAEA's top weapons inspector, Olli Heinonen, said:
"From here on, the IAEA inspectors will have no further access to the reprocessing plant. They plan to introduce nuclear material to the reprocessing plant within a week."
Last month, North Korea threatened to restart the Yongbyon plant. It was angry because of delays in removing the country from the U.S.' terrorism list.
Analysts said it would be several months before North Korea could successfully restart Yongbyon.
Secretary of State Condoleezza Rice, in New York to attend the U.N. Generaly Assembly, issued the following statement:
"We have been through ups and downs in this process before. We believe that for the North Koreans to do so, it will only deepen its isolation."