The official stressed that the threat made at the meeting was not new and he believed Pyongyang would continue to give "careful and serious" consideration to a new US plan to end the nuclear crisis in the Korean peninsula.

The plan was submitted earlier this week at the six-party talks in Beijing involving the United States, two Koreas, China, Russia and Japan.

It would require North Korea to fully dismantle its nuclear arms network in return for multilateral food and energy aid and security guarantees.

North Korean Vice Foreign Minister Kim Gye Gwan met with US Assistant Secretary of State James Kelly in private talks on the second day of the Beijing meeting.

"The threat isn't anything new and came in the context of long and substantive discussion of our proposal and we left the meeting feeling that they would give the plan careful and serious consideration," the official told AFP on condition of anonymity.

The official disputed some news reports quoting a senior administration official as saying that the North Korean threat suggested the Beijing discussions were headed toward failure.

"We told them that nuclear weapons testing was not a constructive response to our proposal," said the official, who is keeping abreast of the US negotiations in the Chinese capital.

"The discussion was not confrontational, threatening or brinksman-like but a long exchange of views and no one left the room in a huff," he said. "It did not come across as an attempt to scuttle the talks."

Nine parties have agreed to provide energy aid to North Korea if it dismantles its nuclear weapons network under the fresh US plan, US State Department spokesman Richard Boucher told reporters Thursday.

He also said that a North Korean plan presented at the six-party talks seeking compensation for a freeze in its illicit nuclear activities would be carefully looked into by the United States.

"We know that nine US parties, some of our friends and allies in the talks, are prepared to provide energy assistance to North Korea, non-nuclear energy assistance, once the program is stopped and we're starting to move down the road," Boucher said.

"And we've all said that if we do move down that road, dismantle the program, that the benefits to North Korea, the possibilities of better relations with us and the others, are certainly opened up quite widely."

Boucher did not name the nine parties but they are believed to include China, South Korea, Japan and Russia.

North Korea's key ally, China, has been the biggest provider of aid to the Stalinist state while US allies Japan and South Korea have also agreed to assist Pyongyang if it accepts the US plan.

It calls for a step-by-step dismantling of North Korea's plutonium and uranium weapons programs in return for aid and security guarantees and easing of its political and economic isolation.

It is also more flexible than previous demands, which had asked North Korea to first completely dismantle its nuclear programs before aid is considered for the impoverished state.

If the plan takes off, the United States said it would begin direct talks about lifting its array of longstanding economic sanctions, and knocking North Korea off its list of terrorist states.

At the Beijing talks this week, North Korea submitted its own "freeze for compensation" package, including verifiable freezing of its nuclear facilities at the Yongbyon nuclear complex.

Inspections would be permitted, but it was not clear whether a complete dismantling of all facilities would follow.

Boucher said the United States "will obviously look very carefully" at the North Korean proposals, which were "very similar" to those submitted in the past and which Washington had responded to previously.

"What's important is that North Korea study carefully the very thorough proposals the United States has put forward to actually achieve the ends that we're discussing at the talks," he said.

WAR.WIRE