Bush "expressed his concern to President Hu" over North Korea's announcement that it plans to restart its atomic reactor at Yongbyon, frozen under six-country negotiations, said spokesman Gordon Johndroe.

And "the two presidents agreed that they would work hard to convince the North to continue down the path established in the six-party talks toward denuclearization," said Johndroe.

The secretive Stalinist state has asked the UN atomic watchdog agency to remove remove seals and surveillance equipment from the Yongbyon facility, IAEA chief Mohamed ElBaradei said Monday.

The North said last week that it was working to restart its atomic reactor at Yongbyon and no longer wanted US concessions promised under the June deal.

The aid-for-disarmament accord is deadlocked by a dispute over verification of the declaration of its nuclear program, which the North delivered as part of the agreement.

The hardline communist regime stopped work to disable its Yongbyon complex last month before confirming last Friday that it was working to restart the plutonium-producing reactor.

North Korea is angry that the United States has failed to drop it from a terrorism blacklist in return for the disablement work.

Washington says it will not do so until it accepts outside inspections to verify the details of the nuclear declaration.

The six-country talks group China, Japan, Russia, North and South Korea, and the United States.