North Korea destroyed the most visible symbol of its nuclear weapons programme today in a sign of its commitment to stop making plutonium for atomic bombs.
The demolition of the 60-foot cooling tower at the North's main reactor complex is a response to US concessions after it yesterday revealed a schedule of its plans to dismantle nuclear ambitions.
The symbolic 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.
Last year, the North switched off the reactor at Yongbyon 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.
But 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 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.
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.
The declaration was being distributed today by China, the chair of the arms talks, to the other countries involved.