YONGBYON, North Korea - North Korea destroyed the most visible symbol of its nuclear weapons program Friday, blasting apart the cooling tower at its main atomic reactor in a sign of its commitment to stop making plutonium for atomic bombs.

An explosion at the base of the cylindrical structure sent the tower collapsing into a cloud of white and gray smoke that billowed into blue skies as international journalists and diplomats looked on, according to video footage filmed by international video news agency Associated Press Television News.

The demolition of the 60-foot-tall cooling tower at the Norths main reactor complex is a response to U.S. concessions after the North delivered a declaration Thursday of its nuclear programs to be dismantled.

"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 Departments top expert on the Koreas who attended the demolition. Kim shook hands with a North Korean official following the towers tumble to the ground.

In its first reaction to the developments this week, North Koreas Foreign Ministry welcomed Washingtons decision to take the country off the U.S. trade and sanctions blacklists.

"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," the ministry said in a statement carried by the official Korean Central News Agency.

The symbolic tower explosion came just 20 months after Pyongyang shocked the world by detonating a nuclear bomb in an underground test to confirm its status as an atomic power. The nuclear blast spurred an about-face in the U.S. hard-line policy against Pyongyang, leading to the Norths first steps to scale back its nuclear weapons development since the reactor became operational in 1986.

Last year, the North switched off the reactor at Yongbyon, some 60 miles north of the capital of Pyongyang, and it already has begun disabling the facility under the watch of U.S. experts so that it cannot easily be restarted.

The destruction of the cooling tower, which carries off waste heat to the atmosphere, is another step forward but not the most technically significant, because it is a simple piece of equipment that would be easy to rebuild.

Still, the demolition offers the most photogenic moment yet in the disarmament negotiations that have dragged on for more than five years and suffered repeated deadlocks and delays.

Secretary of State Condoleezza Rice said the towers destruction would mark a step toward disablement, something that has been ongoing for many months to prevent the North from making more plutonium for bombs.

"It is important to get North Korea out of the plutonium business, but that will not be the end of the story," she said in Kyoto, Japan, on the sidelines of a meeting of the Group of Eight industrialized countries.

North Koreas nuclear declaration, which was delivered six months later than the country promised and has not yet been released publicly, is said to only give the overall figure for how much plutonium was produced at Yongbyon — but no details of bombs that may have been made.

Experts believe the North has produced up to 110 pounds of weapons-grade plutonium, enough for as many as 10 nuclear bombs.

The declaration was being distributed Friday by China, the chair of the arms talks, to the other countries involved, U.S. envoy Christopher Hill said.

"Well have to study it very carefully and then well have to work on verification," Hill said in Kyoto.

The declaration does not address the Norths alleged uranium enrichment program or suspicions of its nuclear proliferation to other countries, such as Syria.

Associated Press writers Jae-soon Chang and Burt Herman in Seoul, South Korea and Matthew Lee in Kyoto, Japan contributed to this report.