SEOUL North Korea toppled the cooling tower at its plutonium-producing reactor on Friday in a symbolic move to show its commitment to an international nuclear deal, a day after submitting an inventory of its atomic program.
Responding to the opening by Pyongyang, the United States moved on Thursday towards taking the North off its list of state sponsors of terrorism and issued a proclamation lifting some sanctions under the Trading with the Enemy Act.
North Korea's actions were in line with a deal with South Korea, China, Japan, Russia and the United States to dismantle its nuclear program in return for an easing of its international isolation.
Video footage showed the some 20-meter (65-ft)-high tower at the Yongbyon nuclear plant being brought down with a blast at its base that sent plumes of smoke into the air and left a crater of rubble and twisted steel.
But experts say key questions remain about North Korea's nuclear weapons and proliferation, and global powers still need to verify the claims in the nuclear declaration, which details the amount of plutonium the secretive state had produced.
In its first reaction since submitting the declaration, North Korea welcomed the U.S. moves to drop it from the terrorism blacklist and called on Washington to halt its hostile policy toward it.
"Only then can the denuclearization process make smooth progress along its orbit," the official KCNA news agency quoted a foreign ministry spokesman as saying.
Steam coming from the cooling tower in spy satellite photographs has been one of the iconic images symbolizing North Korea's decades-long drive for nuclear weapons.
"This was an active reactor. This was a reactor that was making plutonium, that made enough plutonium for several devices including one that was tested in 2006 so it was important to put North Korea out of the plutonium business," said U.S. Secretary of State Condoleezza Rice.
North Korea tested a nuclear device in October 2006.
Lee Chung-min, a professor of international relations at Yonsei University in Seoul, said: "The key issue here is of course verification and what type of an inspection regime the North Koreans agree to.
"Once we come down to the nitty-gritty of inspections, they will basically try to prolong the process as long as possible, without giving up nuclear weapons."
HELP FOR A RICKETY ECONOMY
U.S. President George W. Bush on Thursday cautiously welcomed North Korea's nuclear declaration but warned it that that it faced "consequences" if it did not fully disclose its operations and continue to dismantle its nuclear program.
Once it is removed from the terrorism list, North Korea will be able to better tap into international finance.
Given the small size of North Korea's rickety economy, any increases in investment and trade could have major effects, experts said, adding that increased revenue would likely make its way to Pyongyang's leaders and further solidify their rule.
"It will basically secure their legitimacy and their survivability," said Carl Baker, director of programs at the Pacific Forum CSIS think tank in Hawaii.
Christopher Hill, the chief U.S. envoy to the six-party talks, said in Japan on Friday that all the parties had received a copy of the declaration and would now move to verify its contents.
U.S. officials have acknowledged that the declaration, which came six months after a December deadline, fell short of answering all concerns about Pyongyang's atomic ambitions, especially on past nuclear proliferation activities.
In Washington, State Department spokesman Tom Casey called the tower demolition a positive step.
"What's more important is they continue to finish the rest of the work, including most importantly removing the fuel from the reactor," he said. "And of course certainly we hope to see continued compliance."
MORE TALKS POSSIBLE SOON
South Korean broadcaster YTN cited an unnamed, senior South Korean source as saying that the six-country talks could resume as early as next week.
Foreign ministers from the Group of Eight leading industrialized nations meeting in Kyoto said it was important to speed up the six-way talks and called on the North to take prompt action to answer Japan's concerns about its nationals kidnapped decades ago by North Korean agents.
Under the nuclear deal, Pyongyang was required to start taking apart the ageing Yongbyon plant and provide the nuclear list by the end of 2007.
U.S. and South Korean officials said the North has taken most of the steps to put the Yongbyon facility -- which includes the reactor, a plant to make nuclear fuel and another to turn spent fuel into plutonium -- out of business for at least a year.
Yongbyon is suspected of having problems with safety and radiation contamination. Visitors to the site located about 100 km (60 miles) north of Pyongyang wear protective clothing and are subject to frequent radiation checks.
One source familiar with the plant said it would take years to clean up the contamination but would not speculate if there was any danger from bringing down the cooling tower.
(Additional reporting by Jack Kim in Seoul, Susan Cornwell in Kyoto, Matt Spetalnick, Jeremy Pelofsky and Deborah Charles in Washington, Editing by Jeremy Laurence and Frances Kerry)