North Korea intentionally blew up the most visible symbol of its nuclear weapons program on Friday -- a cooling tower at its main atomic reactor.

The explosion of the 20-metre-tall tower, which was televised, served as an example of North Korea's commitment to stop making plutonium for atomic bombs.

"This is a very important step in the disablement process and I think it puts us in a good position to move into the next phase,'' said Sung Kim, the U.S. State Department's top expert on the Koreas who attended the demolition.

The blast was largely symbolic since the Yongbyon reactor, located 100 kilometres north of the capital of Pyongyang, was disabled last year as part of a deal reached with the U.S., South Korea, China, Japan and Russia.

"It is important to get North Korea out of the plutonium business, but that will not be the end of the story,'' U.S. Secretary of State Condoleezza Rice said Friday in Japan.

On Thursday, North Korea also handed over a long-delayed account of its nuclear work to Chinese officials, prompting the U.S. to lift some trade sanctions against the communist regime.

North Korea's Foreign Ministry welcomed the easing of sanctions saying the "U.S. measure should lead to a complete and all-out withdrawal of its hostile policy toward (the North) so that the denuclearization process can proceed smoothly.''

Foreign Affairs Minister David Emerson outlined Canada's position Thursday, saying "the denuclearization of the DPRK (Democratic People's Republic of Korea) is a matter of strategic interest to Canada."

Friday's explosion comes just 20 months after Pyongyang shocked the global community by detonating a nuclear bomb in an underground test.

Experts believe the North may have produced enough weapons-grad plutonium for as many as 10 nuclear bombs.

With files from The Associated Press