A senior American politician has warned that North Korea and the United States could go to war as early as this year over Pyongyang's alleged nuclear weapons programme.
The prediction of war comes from an authoritative source
William Perry, who served as defence secretary under former President Bill Clinton, told the Washington Post newspaper 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 said.
Later on Tuesday the United States said that North Korean claims that it has produced enough plutonium to start making nuclear bombs were cause for "serious" concern.
White House spokesman Scott McClellan said the US could not confirm the veracity of the claim, but it would not submit to what he described as blackmail.
The warnings came as Chinese envoys held talks with North Korean leader Kim Jong-il amid mounting concerns that North Korea is accelerating its nuclear programme as part of a stand-off with the United States.
The BBC's Rupert Wingfield-Hayes, in Beijing, says China is making it clear the purpose of the visit is to get North Korea back to the negotiating table as soon as possible.
Situation 'out of control'
Mr Perry, who has retained a strong interest in Korean issues, said he believed Pyongyang could soon have enough nuclear devices to test one, or sell material to terrorists.
The situation with North Korea "was manageable six months ago if we did the right things. But we haven't done the right things," the Democrat politician added.
He said he had not criticised President George W Bush's North Korea policy up to now because he hoped the problem was going to be acted on, but he said "time is running out, and each month the problem gets more dangerous".
Reports in recent days suggested the North had finished reprocessing its spent nuclear fuel - the final step in the creation of weapons-grade plutonium for atom bombs. But South Korea says this has not been confirmed.
The BBC's David Bamford, in Washington, says 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.
In the past, President Bush has said he would not allow a nuclear-armed North Korea, but when his spokesman was asked what Mr Bush would now do, he said all options remained on the table.
"It's a serious matter. And that's why we are working closely with the countries in the region and others to address it," Mr McClellan said.
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.
Chinese Deputy Foreign Minister Dai Bingguo handed a letter from President Hu Jintao to Mr Kim, North Korea's official news agency said, and the two "conversed in a cordial and friendly atmosphere".
North Korea's nuclear programme is creating increasing tension
China brokered talks between the US, North Korea and itself in April.
South Korea hopes China can persuade the Pyongyang regime to take part in further peace negotiations, involving regional powers and the United States.
Chinese foreign ministry spokesman Kong Quan said: "We adopt an open attitude to multiple parties being involved. But we believe what's most critical right now is to continue the process of the talks."
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.
The Japanese national daily Asahi Shimbun reported on Tuesday that Mr Dai urged Mr Kim to accept multilateral talks including Japan, South Korea and China, according to unnamed Chinese sources.
The North Korean leader resisted Japan's participation, but was open to South Korea's, the newspaper said.
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.