NEW YORK (AP) — The White House warned today that North Korea would isolate itself from the world community if it backtracks and reactivates the plant that once provided plutonium for an atomic test explosion.

North Korea barred U.N. nuclear inspectors from its main nuclear reactor today, and within a week, it plans to reactivate the plant that once provided the plutonium for the explosive test two years ago, the chief U.N. nuclear inspector said. North Korea ordered the removal of the U.N. seals and surveillance equipment from the Yongbyon reactor, a sign it is making good on threats to restart its nuclear program.

“The North Korean actions are very disappointing,” said White House spokesman Gordon Johndroe from New York.

Johndroe said North Korea’s actions run counter to the “six-party talks,” the process by which North Korea agreed to pursue nuclear disarmament in exchange for diplomatic concessions and aid. Beyond the U.S. and North Korea, the other parties in those talks are South Korea, China, Russia and Japan.

“We strongly urge the North to reconsider these steps and come back immediately into compliance with its obligations,” Johndroe said.

The nuclear reversal has fueled worries about a breakdown of international attempts to coax the North out of its confrontational isolation with most of the rest of the world.

North Korea officials have “informed the IAEA inspectors that they plan to introduce nuclear material to the reprocessing plant in one week’s time,” said a statement citing Mohamed ElBaradei, the chief of the International Atomic Energy Agency.

North Korea had agreed in February 2007 to begin dismantling its nuclear program in exchange for aid and other concessions.

Scientists began disabling its reactor in November, and in June blew up the Yongbyon cooling tower in a dramatic show of its commitment to the pact. Eight of the 11 steps needed to disable the reactor were completed by July, North Korean officials said.

But later that month, Washington made an additional request: detailed verification of the process, including soil samples and interviews with scientists. The U.S. pinned one of its concessions — removing North Korea from its list of nations that sponsor terrorism — on verification. The process has since stalled.