Yongbyon, North Korea ? The gray cooling tower crumbled behind billowing dust clouds in seconds Friday, reducing the structure at North Korea’s nuclear reactor into a pile of rubble. It was a choreographed show by the communist regime meant to affirm an intention to stop making atomic bombs.

From a distance, smiling diplomats from the United States and other nations snapped photos of the blast that destroyed part of the heart of the North’s nuclear weapons program.

“As you all saw, the cooling tower is no longer there,” said Sung Kim, the U.S. State Department’s top expert on the Koreas who attended the demolition. “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.”

The 60-foot-tall cooling tower at the Yongbyon nuclear center had been the most visible symbol of the North’s nuclear program and a focus for U.S. satellite surveillance. Steam spewing from the tower meant that the North’s main nuclear reactor was operating to make plutonium.

Just before detonation, red warning flares were fired into the clear sky. At 3:10 a.m. CDT, an explosion at the base of the tower sent it collapsing into a cloud of dust and smoke that blew over grassy fields along a small river.

After the explosion, the site was littered by broken columns of reinforced concrete and other shattered pieces of the tower shown in video of the site by international video news agency Associated Press Television News.

The tower’s destruction was not mentioned by the North’s media or shown on state TV broadcasts.

Ri Yong Ho, director of safeguards at North Korea’s Academy of Atomic Energy Research, was the most senior Pyongyang official present and shook hands with Kim after the blast.

“The demolition of the cooling tower is proof that the six-party talks have proceeded a step further,” Ri said, referring to the nuclear disarmament negotiations.

Blowing up the tower was intended to demonstrate North Korea’s commitment to forgo atomic weapons ambitions that culminated with its first nuclear test detonation in 2006.

Its destruction came in response to U.S. concessions announced Thursday to remove Pyongyang from terrorism and sanctions blacklists after the North delivered a long-awaited declaration of its nuclear programs.