By Jonathan Marcus
Diplomatic correspondent, BBC News
The announcement that Mohamed ElBaradei, the head of the International Atomic Energy Agency, has been invited to visit North Korea represents the most important tangible sign yet that the so-called six-party agreement reached on 13 February in Beijing is actually being implemented.
The goal of this agreement, involving North and South Korea, China, Russia, the United States and Japan is to resolve not only the controversy over Pyongyang's nuclear weapons programme, but also other outstanding regional issues between the two Koreas, between North Korea and Japan, and between Pyongyang and Washington.
North Korea has pledged to shut down its main reactor at Yongbyon
The deal has a tight initial timeline. Certain steps must be taken by the North Korean authorities within 60 days.
The nuclear reactor at Yongbyon must be shut down and sealed and international inspectors must be allowed back to verify what is going on.
For that there has to be agreement on the scale and scope of the IAEA's activities.
So the invitation to Mr ElBaradei is an initial indication at least that Pyongyang is serious about implementing its side of the deal.
The six-party process has been fraught with difficulty. Expectations were not high and sceptics - especially more hawkish voices in Washington - have engaged in a drumbeat of criticism of the deal.
But the thinking behind it represents a significant shift in the US position.
Is Kim Jong-il serious or simply going through the motions?
The Bush Administration is pursuing more of a step-by-step approach. This has the benefit of drawing Pyongyang into a network of talks by establishing short-term deadlines in which potentially real progress can be made.
If all of the initial 60-day goals are reached then there will be a meeting of the six nations' foreign ministers in Beijing, probably in April.
There are still a lot of hurdles along the way. Nothing has so far been said about North Korea's existing nuclear arsenal - it is thought to have several warheads stored away.
And disputes about a second, parallel nuclear weapons programme based on uranium enrichment could easily de-rail the wider process.
Nonetheless, in a step that confounded the sceptics an initial deal has been reached.
Is Pyongyang serious, or is it simply going through the motions?
It is now up to Mr ElBaradei, amongst others, to find out and put flesh on the bones of the agreement reached earlier this month.