"Because North Korea has cheated in the past, verification to check on what North Korea says is going to be very robust," Albright told CNN.

However, the US nuclear analyst welcomed North Korea's handover of its nuclear declaration to China.

"It's a very significant development. For many months North Korea has been taking action. They've disabled or destroyed -- probably destroyed facilities at their complex. They turned over thousands of pages of operating records for the United States to peruse," Albright told CNN in an interview.

But, the US nuclear analyst said, "there is a lot of work left to do."

The declaration describes how much plutonium has been produced, and how much has been turned into a form usable for nuclear weapons, "but they didn't show them the weapons or the plutonium," Albright said.

Washington accuses Pyongyang of having broken its word on the 1994 US-North Korea Agreed Framework pact.

But Albright said recent events showed the two sides "starting to work together" instead of perceiving one another "in absolutely evil terms" as in the past.

The North on Thursday delivered its long-overdue 60-page declaration of its nuclear material and programmes -- but not weapons -- to China, which hosts six-nation disarmament negotiations that began in 2003.

On Friday it plans to blow up Yongbyon's cooling tower in front of a worldwide TV audience, to symbolize its apparent commitment to denuclearization.