North Korea is preparing to demolish the cooling tower at its Yongbyon nuclear reactor, in a symbolic display of its intention to disarm.
The move comes a day after the isolated state handed over long-awaited details of its nuclear programme.
In return, US President George Bush agreed to scrap some of its sanctions against North Korea, and remove it from a list of states sponsoring terrorism.
Former US envoy to the UN, John Bolton, said Mr Bush's decision was "shameful".
He said the move represented the "final collapse" of the Bush administration's foreign policy.
But others have welcomed the actions of both Pyongyang and Washington, with analysts saying that recent developments appear to have breathed new life into the long-running six-party talks on disarming North Korea.
The talks have stalled repeatedly since an agreement was reached 16 months ago, in which the North agreed to scrap its nuclear ambitions in return for aid and diplomatic concessions.
Russia has suggested restarting the meetings - which include representatives from North and South Korea, Japan, China, the US and Russia - as early as next week.
Televised demolition
North Korea has invited international television crews to witness the demolition of the cooling tower.
While analysts say that the destruction of the tower is not, in itself, a huge step forward, it is still being seen as an important symbolic gesture.
According to the BBC's correspondent in Seoul, John Sudworth, it is a spectacular demonstration of the North's intention to give up production of weapons-grade plutonium.
North Korea agreed to put its nuclear facilities beyond use as part of the six-party agreement reached in February 2006.
The handing over of a document detailing the North's nuclear activities was also part of this agreement.
The long-awaited document was handed over to Chinese delegates o Thursday, and chief US negotiator Christopher Hill said on Friday that copies had also been sent to other nations involved in the negotiations.
"We have to study it carefully and we will have to work on the verification," Mr Hill told the French news agency AFP.
The document is six months overdue and is not certain to satisfy the international community.
It is expected to cover the North's plutonium production activities, but analysts believe it will not address other key issues including a suspected uranium enrichment programme - which, like plutonium, could also be used to make nuclear weapons.
Another potential stumbling block is the allegation that the North helped Syria to build a nuclear facility - a claim denied by Pyongyang.
And the possibility that the country has already managed to build a small number of weapons has not even been touched on yet, according to the BBC's diplomatic correspondent Jonathan Marcus.
US concessions
As a result of the North's decision to hand over the document, President Bush not only pledged to lift some sanctions on the North, but he also said he would remove the regime from its list of state sponsors of terrorism.
Removal from the terror list would pave the way towards lifting many of the most stringent sanctions, and enables Pyongyang to start receiving low-interest loans from the World Bank and other international lending agencies.
While making these pledges, Mr Bush emphasised that moves to take the country from the terror list would not begin for 45 days, and would start only if the North's claims were verified.
"We remain deeply concerned about North Korea's human rights abuses, uranium enrichment activities, nuclear testing and proliferation, ballistic missile programmes and the threat it continues to pose to South Korea and its neighbours," he said.
"It will remain one of the most heavily-sanctioned nations in the world."
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