President Bush, in a call with Chinese President Hu Jintao, expressed his concern over North Korea's plans to re-open the Yongbyon nuclear reactor, the White House said Monday.

"The two presidents agreed that they would work hard to convince North Korea to continue down the path established in the Six Party Talks toward denuclearization," White House national security council spokesman Gordon Johndroe said.

This came as North Korea asked the IAEA to remove seals and surveillance equipment from the Yongbyon nuclear reactor, the agency chief said Monday, heightening concerns that the communist nation may be preparing to restart its nuclear program.

International Atomic Energy Agency chief Mohamed ElBaradei told the 35-nation IAEA board that North Korea said it wanted to "carry out tests at the reprocessing plant, which they say will not involve nuclear material."

Still, the move suggested the country was making good on its threat last week to restart the nuclear program, which led to an underground nuclear test blast nearly two years ago,

North Korea had said that it was making "thorough preparations" to start up Yongbyon, which it began disabling last year under a now-stalled disarmament-for-aid deal.

"Some equipment previously removed by the DPRK during the disablement process has been brought back" to Yongbyon, ElBaradei told the closed meeting in comments made available to reporters. DPRK is the abbreviation of North Korea's official name, the Democratic People's Republic of Korea.

While the reactor remains shut down, "this morning, the DPRK authorities asked the agency's inspectors to remove seals and surveillance equipment," he said.

The agency has been monitoring the nuclear facilities at Yongbyon, which were shut down and then sealed as part of a North Korean pledge to disable its nuclear program. That move was meant to be a step toward eventual dismantling Yongbyon in return for diplomatic concessions and energy aid equivalent to 1 million tons of oil under a February 2007 deal with South Korea, the U.S., China, Russia and Japan.

On Monday evening however, a senior US defense official told FOX News that there wasn't any intelligence suggesting that the equipment has been reinstalled at the reprocessing plant or any attempt to restart the plant has been made.

The accord hit a snag in mid-August when the U.S. refused to remove North Korea from its list of states that sponsor terrorism until the North accepts a plan to verify a declaration of its nuclear programs it submitted earlier.

The Yongbyon reactor was under IAEA seals in December 2002 when the North decided to order IAEA inspectors out of the country and restart its mothballed nuclear activities, after a deal committing the U.S. to help Pyongyang build a peaceful nuclear program unraveled.

It subsequently quit the Nuclear Nonproliferation treaty in January 2003 and announced it had nuclear weapons a little more than two years later.

FOX News' Mike Emanuel, Daniela Sicuranza and The Associated Press contributed to this report.