VIENNA (Reuters) - North Korea's agreement to allow inspections of its Yongbyon nuclear plant is a welcome emergence from isolation, but far from enough to reassure the world it will give up its ambitions for nuclear weapons, diplomats and experts say.
North Korea said on Wednesday it would suspend nuclear tests, long-range missile launches and enrichment of uranium at its Yongbyon facility and allow back International Atomic Energy Agency personnel. The surprise turn of events also brings U.S. food aid for the impoverished state and makes possible the resumption of six-nation nuclear negotiations with Pyongyang.
It was unclear how much scope for inspections the Vienna-based U.N. agency would get - the North has limited their access during two previous periods when it allowed inspectors in.
And Western analysts said the Asian country may simply continue covert atomic activity elsewhere.
"I assume North Korea would try to limit the IAEA's role as much as possible," said Mark Fitzpatrick, an expert on nuclear proliferation. "North Korea has always been suspicious of the IAEA."
Like other Western diplomats, a European based in the Austrian capital said the North's agreement to let international monitors back to Yongbyon was a "very positive step" as the complex was the primary focus of its nuclear programme.
But, the envoy added: "Who knows what might have been built off site."
Members of a U.N. expert panel said in a confidential report last year that North Korea most likely had several more undisclosed enrichment-related facilities, in addition to the one at Yongbyon revealed in late 2010.
In an ideal situation for the outside world, Pyongyang would let the IAEA "essentially map the entire history and current situation" of the nuclear programme, said Mark Hibbs of the Carnegie Endowment for International Peace.
But more likely, he said, was that it would "continue to develop a clandestine enrichment capability including facilities which are not declared and known to the IAEA".
Analysts cautioned that Pyongyang had reneged on past deals, but noted its latest move marked a sharp change in course by the reclusive state after the death in December of new leader Kim Jong-un's father, veteran strongman Kim Jong-il. U.S. officials said persistence and patience were needed.
"I believe it is very unlikely that North Korea will give up its nuclear weapons," said Jeffrey Lewis, a director of the James Martin Center for Nonproliferation Studies in California.
"But we have no choice but to try."
The Yongbyon complex is at the heart of North Korea's plutonium weapons programme. It includes a reprocessing plant where weapons-grade material is extracted from spent fuel rods.
In late 2010, foreign experts said North Korean officials had shown them a uranium enrichment facility at Yongbyon, potentially offering a second path to make bombs.
Fitzpatrick, at London's International Institute for Strategic Studies, said it was "widely assumed" that North Korea could not have established this site without having at least a pilot plant elsewhere, as well as a uranium conversion facility.
Of Yongbyon, he said: "The IAEA will be able to see the uranium enrichment facility, will be able to monitor the suspension of activity and presumably will also learn something about it, how far along they were, this will be very useful to know."
But, Fitzpatrick added, Pyongyang had not declared the suspected "hidden facilities and work presumably would continue" in such locations.
Shannon Kile of the Stockholm International Peace Research Institute (SIPRI) said of the North Korean authorities: "I just cannot imagine that the DPRK would allow the IAEA to undertake inspections to verify the absence of undeclared activities.
"That would surprise me very much."
To be certain that no material is diverted for military purposes, analysts said inspectors would need full access to all uranium enrichment activities. This would usually mean frequent inspections, video cameras and special seals at such sites.
Former U.N. chief inspector Olli Heinonen said that although this week's suspension announcement was a positive step, North Korea "has still to place all nuclear material and facilities under the IAEA safeguards".
The IAEA, whose mission is to prevent the spread of nuclear weapons in the world, is believed to have a team of inspectors who are North Korea specialists and are prepared to go to the country at short notice.
Dozens of its inspectors - who form part of a department which also has its hands full with Iran's disputed nuclear programme - have past experience of working in North Korea.
One Vienna-based ambassador, asked about the restrictions the agency may face in North Korea, said: "We have to face reality. To do something is better than nothing."
North Korea kicked out international inspectors a decade ago when a 1994 deal between Pyongyang and Washington unravelled. It expelled them again in April 2009 after rejecting the intrusive inspections agreed under a 2005 aid deal with five regional powers that allowed the watchdog to return.
Clearly hoping for more success this time, IAEA chief Yukiya Amano hailed Wednesday's news as "an important step forward" and said the agency stood ready to return to Yongbyon upon request and with the agreement of its 35-nation board of governors.
Diplomats said it was now up to North Korea to contact the U.N. agency about its resumption of inspection work. It was unclear, they said, whether the issue would be discussed as soon as the board's next regular meeting on March 5-9.
"It's up to the North to do the first reach-out to Director General Amano," a senior U.S. official said. "I have no doubt that there will be some tough negotiations going forward in terms of exact sequencing" of a Pyongyang-Washington accord.
Editing by Kevin Liffey and Alastair Macdonald