North Korea destroyed the most visible symbol of its nuclear weapons program Friday, blasting the cooling tower at its main atomic reactor into a cloud of white and gray smoke as 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 debris and dust that billowed into blue skies as journalists and diplomats looked on, according to footage filmed at the site by international video news agency Associated Press Television News. Those who watched the demolition later pored over the shattered pieces of the tower. The demolition of the 60-foot-tall cooling tower at the North's main reactor complex is a response to US concessions after the North delivered a declaration Thursday of its nuclear programs to be dismantled. Hours after the blast, North Korea's government praised Washington's moves to lift sanctions but also called on the US to completely abandon its "hostile policy" against the regime. "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 US State Department's top expert on the Koreas who attended the demolition. Kim shook hands with a North Korean official following the tower's tumble to the ground. In its first reaction to the developments this week, North Korea's Foreign Ministry welcomed Washington's decision to take the country off the US trade and sanctions blacklists. "The US 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 US hard-line policy against Pyongyang, leading to the North's 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 has already begun disabling the facility under the watch of US 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. US Secretary of State Condoleezza Rice said the tower's 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 Korea's 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 (50 kilograms) 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, US envoy Christopher Hill said. "We'll have to study it very carefully and then we'll have to work on verification," Hill said in Kyoto. South Korea's nuclear negotiator Kim Sook told reporters in Seoul that the disablement process would take several more months to complete, and that countries at the negotiations were discussing when to convene the next round. The declaration does not address the North's alleged uranium enrichment program or suspicions of its nuclear proliferation to other countries, such as Syria.