By Charles Scanlon
BBC News, Seoul
Officials from the International Atomic Energy Agency (IAEA) have been back to North Korea's nuclear complex at Yongbyon for the first time in nearly five years.
Yongbyon has long been at the centre of international concern
North Korean leader Kim Jong-il appears ready to comply with an international agreement reached in February to shut down key facilities at the site.
The US and others are now bearing diplomatic gifts for the once reviled regime in Pyongyang.
Why such an apparently benign turn of events after years of confrontation?
The decisive change has been in the policy of the Bush administration, which has dropped its pressure tactics and dreams of regime change, and switched to engagement.
Officials and analysts say there is no indication, on the other hand, that North Korea has made a strategic decision to give up its nuclear arsenal - which some estimates say consists of as many as 12 crude atomic bombs.
"The North Koreans will never give up their nuclear weapons," North Korea watcher, Andrei Lankov of Kookmin University in Seoul, says.
"They thrive on tension and use it to prevent an opening of their country to the outside world."
Some believe that North Korea is interested in limited engagement, but will not surrender a nuclear deterrent on which it has invested so much diplomatic energy and scarce resources.
After years of blood-curdling threats, US officials and IAEA inspectors are now being greeted by the smiling face of the world's most isolated and militaristic nation.
That is because the North Koreans think they are on the verge of a major diplomatic victory, and they expect their nuclear gambit to continue paying dividends for years to come.
IAEA inspectors have spoken positively of their Pyongyang visit
Only after North Korea tested its first nuclear device last October did the Bush administration resolve (for now) its internal policy differences on the North.
After sponsoring a largely symbolic resolution at the UN Security Council, Washington eased back on what North Korea used to call its "hostile policy".
The administration dropped its long held opposition to bilateral talks, and swallowed its pride by returning North Korean money frozen in a Macau bank - some of which, the US Treasury alleged, came from the proceeds of "criminal activities", including the counterfeiting of US dollars.
Five years ago, the reactor at Yongbyon was in mothballs and IAEA monitors were in place.
Everything changed in October 2002, when the US accused North Korea of running a second, secret, nuclear programme based on the enrichment of uranium.
The US cut off supplies of fuel oil, which it had been shipping under the Agreed Framework of 1994. In retaliation, the North Koreans threw out the inspectors and fired up their old plutonium programme at Yongbyon.
Crucially, they also reprocessed the large pile of nuclear fuel that had been kept under observation under the old agreement.
Now, it is back to square one again, but with one major difference: North Korea has used the years of confrontation to race ahead with its once-frozen plutonium programme.
It tested a nuclear device (with limited success) in October 2006 and now has enough plutonium for several more.
Significantly, it has still not acknowledged the existence of the alleged uranium programme- an alternative route to a nuclear bomb - which sparked off the confrontation in the first place.
US negotiators argue that the new agreement goes further than the Agreed Framework.
They say that North Korea has agreed to "disable" and not just freeze its nuclear facilities. And they say it has agreed to come clean about the whole range of its nuclear activities - including the alleged uranium programme.
Victor Cha, until recently the head of Asia at the National Security Council and Christopher Hill's number two in the US negotiating team, says he doubts the North will give up the nuclear weapons it has already built.
"Anyone in the US government who's been involved in negotiations with the North Koreans won't go into this with rose tinted glasses. The assumption has to be that they intend to trade away parts of their nuclear programme but keep a residual arsenal of nuclear weapons," he said.
Change of tack
The Bush administration's initial policy was to try to get key region powers to put pressure on North Korea to disarm.
It said there would be no rewards for bad behaviour and demanded the "complete, verifiable and irreversible dismantlement" of all nuclear programmes without conditions.
The demand came to be known as CVID - but no-one talks about that anymore.
The six-party talks were conceived in Washington to confront North Korea with a united front of all its neighbours and the US.
That approach failed to stop North Korea going nuclear, and it was the US that became isolated. China and South Korea in particular worried that too aggressive an approach could provoke a violent backlash.
Washington's new flexibility and willingness to negotiate with the North Koreans is in part an effort to win back confidence in a region grown wary of a distracted and inconsistent US.
"We were always told by officials in the region to show political will and a commitment to diplomacy," says Victor Cha. "Well we're showing political will now. We need to prove that we're serious and if the agreement fails it's because North Korea never intended to implement it."
The US says its intention now is to test North Korea's commitment.
Sceptics worry that it will play into the hands of a regime that is a master of ambiguity and delaying tactics.
N KOREA NUCLEAR DEAL
N Korea to "shut down and seal" Yongbyon reactor, then disable all nuclear facilities
In return, will be given 1m tons of heavy fuel oil
N Korea to invite IAEA back to monitor deal
Under earlier 2005 deal, N Korea agreed to end nuclear programme and return to non-proliferation treaty
N Korea's demand for light water reactor to be discussed at "appropriate time"
The February agreement is very vaguely worded and provides plenty of scope for prevarication and dispute. Every inch of ground is likely to be contested and North Korea is sure to extract the maximum price for each concession.
Keeping up the pressure will prove difficult. South Korea and China are relieved that the confrontation is now receding, along with the danger of armed conflict or a collapse of the regime in Pyongyang.
They believe that the nuclear dispute can be managed and contained over a long period - if only Washington's impatience can be held in check.
The regime in Pyongyang sees the nuclear card as the key to its survival. It has played a seemingly weak hand with practiced skill - successfully driving wedges between its immediate neighbours and the US.
It is a strategy that could keep the regime ticking over for years, ensuring badly-needed handouts from nervous neighbours, and postponing the day when reform and an opening to the outside world must surely come.