"During this period, the United States will carefully assess North Korea's actions particularly with regard to verification," she said.

Pyongyang has also pledged to destroy a cooling tower at its main Yongbyon nuclear complex on Friday, a White House statement said.

'More information needed'

North Korea has to do more to encourage a further removal of restrictions, Perino said.

"There is still more work to be done in order for North Korea to end its isolation.

"It must dismantle all of its nuclear facilities, give up its separated plutonium, and resolve outstanding questions on its highly enriched uranium and proliferation activities. It must end these activities in a fully verifiable way." 

The North Korean report is a truncated version of a declaration originally sought by Washington.

Melissa Chan, Al Jazeera's correspondent in Beijing, said: "What we are seeing is a report that does not answer any questions about the North Koreans' nuclear enrichment programme; it does not specifically say how many nuclear warheads they have. So there is an avoidance of issues here.

"Even though the Americans have been counting this [report] as progress, some critics say the report is not a full disclosure of what the North Koreans have been up to in the past few years.

"Others say the six-party talks are a diplomatic process that will last for some time and any sort of development of this kind should be welcomed as a positive move."

Nuclear pledge

The handover of the North Korean declaration is a significant step in the implementation of a six-party nuclear disarmament pact signed early last year.

China hosted talks that secured the deal offering North Korea diplomatic and economic incentives to disable its main nuclear facility and declare all related programmes.

The US' removal of North Korea from their terrorist sponsor list could ease international trade and financial restrictions, as well as improving ties between Pyongyang and Washington.

Japan has expressed unease over the North being taken off the US blacklist before the issue of its citizens being kidnapped by Pyongyang is resolved.