North Korea toppled the cooling tower at its Yongbyon nuclear plant today, in a dramatic display which the secretive regime hoped would show its commitment to a nuclear deal.

However, experts say the televised event still leaves unanswered questions about the North's nuclear programme and capabilities.

The United States, keen to head off suggestions of a U-turn after it removed North Korea from its list of terrorist states yesterday, warned the secretive Communist state that it faced “consequences” if it did not fully disclose its operations. Yesterday, the regime handed over a limited list of its atomic capabilities, which critics said lacked sufficient detail.

Yesterday, President Bush moved to expunge North Korea from Washington’s list of state sponsors of terrorism, and issued a proclamation lifting some sanctions under the Trading with the Enemy Act, which it has applied to North Korea since the 1950-1953 Korean War.

The destruction of the tower today, designed to produce arms-grade plutonium, was witnessed by five foreign TV stations who later broadcast footage of the event.

It was originally scheduled to be broadcast live by international media, with CNN at the top of the guest list, but TV stations reported technical problems at the scene.

The complex, 60 miles north of Pyongyang, is at the heart of US-led six nation talks aimed at shutting North Korea’s nuclear programme in exchange for energy aid and major diplomatic and security benefits.

Yongbyon produced the plutonium for an atomic weapons programme which culminated in a nuclear test in October 2006. It was shut down in July 2007 as part of an agreement procured at the six-way talks.

Analysts have questioned the significance of the tower's destruction, as the plant has already produced enough plutonium for a small nuclear arsenal, details of which are not thought to be included the inventory submitted yesterday.

Meanwhile North Korea's success in moving towards better relations with the United States - despite having over the years ceded less ground on its nuclear programme than Iran and Saddam Hussein's Iraq, the two other countries named on Mr Bush's axis of evil - could be seen as sending a message to rogue states that developing a nuclear arsenal is the surest way to force concessions from Washington.

Christopher Hill, the chief US envoy to the six-party negotiations, said in Japan today that all the parties had received a copy of the declaration and would now move to verify its contents.

South Korea’s Foreign Minister Yu Myung-Hwan said the parties - the two Koreas, the United States, Russia, China and Japan - were holding consultations about a new meeting, with a target date of early July.

North Korea’s disclosure of its nuclear activities could mark a breakthrough in relations both with its democratic neighbour South Korea and with Western powers such as the United States.

But there were signs today that both Seoul and Washington would take a cautious approach towards warming ties.

North Korea has a history of failing to implement agreements, or failing to live up to their provisions. More hitches on denuclearisation may be in store despite this week’s progress.

Condoleezza Rice, the US Secretary of State, told reporters at G8 talks in Japan that "serious questions" still remained.

"The North Koreans have already made available thousands of pages of documentation on the Yongbyon reactor. We also need access to the reactor core and to the waste pool to verify the numbers the North Koreans have already given us. That's an example of the kind of verification we expect," she said.

"We also have serious questions about uranium enrichment and proliferation questions. The President said yesterday he'd notified Congress of our intention to remove this state from the Enemies Act sanctions, but the DPRK remains under multiple sanctions regimes. There are Security Council resolutions, human rights, and proliferation. There are very many sanctions still in place."

She added: "Obviously we have the capacity to bring about future consequences if the North does not live up to its obligations."

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