The US said that North Korean claims it has produced enough plutonium to start making nuclear bombs were cause for serious concern.

Although the White House said it could not confirm the veracity of the claims, it said it would continue to work with China, Japan and South Korea to stop North Korea?s nuclear weapons programme.

North Korea claimed to have completed the reprocessing of 8,000 spent fuel rods to extract plutonium for nuclear weapons at a diplomatic meeting in New York last week. The Chinese media yesterday reported that Foreign Minister, Li Zhaoxing had discussed the crisis by telephone with the US Secretary of State, Colin Powell.

?The two sides agreed to keep contact and exert efforts to further the Sino-US constructive and cooperative relationship,? the agency said, but gave no future details.

Meanwhile a senior American politician has warned that the US could go to war with North Korea as early as this year over Pyongyang?s alleged nuclear weapons programme.

William Perry, who served as Defence Secretary under former president Bill Clinton, said the key issue was that North Korea appeared to have begun reprocessing spent nuclear fuel rods, a key step towards building up its nuclear arsenal.

?I have thought for some months that if the North Koreans moved toward processing, then we are on a path toward war,? he told the Washington Post newspaper.

US warning ?The White House has acknowledged that it does not know for sure whether this latest North Korean claim is genuine or bluster, but the fact that Pyongyang is saying it at all is serious. That is why we are working closely with the countries in the region and others to address it,? White House spokesman, Scott McClellan said. North Korea has a clear choice between two paths.

?The international community has made clear that continued pursuit of nuclear weapons will only lead to further isolation and a deteriorating situation for the regime in Pyongyang.?

Asked whether George W. Bush might resort to military force against North Korea, Mr McClellan said: ?The president never takes options off the table, but it?s something that we want to address in a multilateral way.?

The warnings came as Chinese envoys held talks with North Korean leader, Kim Jong-il, amid mounting concerns over North Korea?s nuclear programme.

In Beijing, China is making it clear the purpose of the visit is to get North Korea back to the negotiating table as soon as possible.

China has been under pressure to use its influence, as one of the North?s closest allies, to help broker a negotiated solution to the crisis, which has destabilised the region since last October.

South Korea hopes China can persuade the Pyongyang regime to

take part in further peace negotiations, involving regional powers and the United States.

One-to-one talk

But North Korea, which blames Washington for provoking the crisis, has insisted on one-to-one talks with the US alone, something Washington is reluctant to contemplate.

Diplomats say China offers the best hope of a negotiated settlement, not least because North Korea depends on China for the bulk of its food and fuel.

China has an interest in the issue, because it does not want a nuclear-armed North Korea in its backyard, but neither does it want Kim Jong-il?s regime to collapse, which could result in millions of refugees flooding over its border.

Questions &answers

• What is this crisis all about?

Relations between the US and North Korea have deteriorated since President George W. Bush labelled North Korea part of an "axis of evil" in January 2002. Tensions really started escalating in October, when the US accused North Korea of developing a secret nuclear weapons programme. Since then North Korea has restarted a mothballed nuclear power station, thrown out inspectors from the UN's International Atomic Energy Agency and pulled out of the Nuclear Non-proliferation Treaty. It has also upped its frequently doom-laden rhetoric, warning of the risk of nuclear war. It is often very difficult to tell what lies behind North Korea's moves. Pyongyang and its mercurial leader Kim Jong-il act in erratic and contradictory ways. But it seems possible that North Korea has been trying to use the nuclear issue as a hard-line ploy to negotiate a non-aggression pact and improved economic aid from the US. Alternatively, the paranoid North may have decided the US intends to attack it anyway and has been readying its defences while the US was preoccupied with Iraq.

• Can diplomatic talks resolve it?

Maybe, but not easily. Almost everyone ? except North Korea ? agrees the secretive state should not be allowed to continue with its nuclear weapons programme. The difficulty will be finding enough diplomatic and economic carrots to persuade North Korea's leaders to give the programme up. The Bush administration is especially wary because North Korea has broken exactly that kind of nuclear deal before, in 1994. And although the North's most pressing problem is its moribund economy, Kim Jong-il's first concern is the survival of himself and his military backers. From his perspective, he is being asked to give up his only guarantee against US attack, nuclear weapons.

• What do we know about North Korea's nuclear weapons programme?

According to US accounts, the North Koreans admitted that they had a nuclear weapons programme at a meeting in October 2002 with Assistant Secretary of State, James Kelly, in Pyongyang. Again according to the US, a North Korean negotiator told Kelly in April 2003 that the North had nuclear weapons. Publicly, North Korea has merely said it retains "the right" to have such weapons. Most arms control experts suspect North Korea of pursuing an active weapons programme ? certainly up to 1994, when it signed a landmark agreement to freeze all nuclear-related activities. In December 2002, North Korea restarted its nuclear reactor at Yongbyon and forced two IAEA monitors to leave the country. As a result, the outside world cannot be sure as to how far work has progressed at Yongbyon. If it was fully operational, some analysts believe it could produce enough plutonium to build another bomb within a year or two. America's CIA says a separate, enriched uranium programme could be producing "two or more" bombs each year by the middle of this decade.

• How many weapons does North Korea already possess?

This is very hard to say without the IAEA inspections. Experts believe that North Korea may have extracted sufficient plutonium for a small number of bombs. US officials have put the number at "one or two". Spent fuel rods that were put into storage in 1994 could also be used to extract plutonium for a handful of weapons, the US believes.

• Should we be worried?

Yes. Arms proliferation matters, especially when weapons of mass destruction fall into the hands of secretive, unpredictable regimes which may well be heading for catastrophic failure. Many experts believe that the North Korean system is in terminal decline. Its people suffer great poverty and frequent famine. How the regime ends matters, and managing this potential crisis is made harder if it has nuclear arms. There is also the danger that an unstable regime like this could provide such weaponry to third parties. North Korea already has a bad track-record in the proliferation of missile technology.

• What difference does the US see between North Korea and Iraq?

They are different cases. North Korea is already an isolated regime with huge domestic problems. Two of America's regional allies ? South Korea and Japan ? have an active policy of engagement to try to win Pyongyang round to a more compliant line. Perhaps more importantly, North Korea is believed to have the bomb, while Iraq did not. The view in the Bush administration is that action has to be taken before a country gets a nuclear capability. With North Korea it is just too late, so Washington has to manage the consequences as best it can.