"It's not the first time that the North Koreans have talked about showing their deterrent," a White House official said on condition of anonymity while aboard President George W. Bush's jet en route to Ireland and a NATO summit in Istanbul.

North Korea's chief delegate to six-party talks in Beijing on the Korean nuclear crisis told his US counterpart on Thursday that some quarters in Pyongyang were keen to conduct a nuclear weapons test, indicating a power struggle within the isolated communist regime.

The two-and-a-half-hour meeting between Vice Foreign Minister Kim Gye Gwan and US Assistant Secretary James Kelly took place just after Washington submitted a new plan at the Beijing meeting for a step-by-step dismantling of North Korea's plutonium and uranium weapons programs in return for aid and security guarantees.

The US plan was coordinated with China, South Korea and Japan, which, along with Russia and North Korea make up the six-party conference which ends on Saturday.

The White House official said "it would be an extremely odd time, given that they've (the North Koreans) just been given a different path that they might be able to take, to do something of that kind.

"But, you know, they make those threats from time to time and they just serve to further isolate them," said the official.

The State Department said Kim's remarks indicated "some in Pyongyang wanted to test a nuclear weapon."

It should not be seen as a threat or an ultimatum, said Adam Ereli, the department's deputy spokesman.

"Rather, to the contrary, I think we came away from this long and involved and engaged discussion with the firm view that the North Koreans are going to give our proposal very serious consideration," he said.

Ereli dismissed reports quoting a senior US official Thursday that Kim's disclosure would jeopardise the six-party negotiations.

"I would not concur with that assessment," Ereli said.

As White House and State Department officials played down Pyongyang's threat, reports emerged in Tokyo that North Korea may have tested a short-range missile this week just before the six-party talks began in Beijing Tuesday.

The United States told Tokyo the missile was fired towards the Sea of Japan Tuesday from the east coast around Tanchon, in South Hamgyong Province, Kyodo news agency reported, quoting sources familiar with Japan-US ties.

The missile may have been a land-to-ship Silkworm missile or ballistic missile "smaller than a Scud", the US Defense Department reportedly told its Japanese counterparts.

The report could not be immediately confirmed in Washington.

It was also not clear if the reported test was meant as a warning ahead of the talks or simply part of Pyongyang's ongoing missile program.

The US also warned a second missile might be launched, the sources added, but did not say how they had gained the information or how far the missile reportedly tested this week had flown.

North Korea reportedly test-launched land-to-ship missiles at least six times between February and October last year.

Ereli said Washington remained concerned about North Korea's nuclear weapons programs and proliferation.

"We have made clear that concern," he said.

Amid a collapsing economy, North Korea's only bargaining chip is its nuclear weapons.

Two previous rounds of six-party talks hosted by China have failed to narrow differences on how to end the 20-month-old crisis after Washington accused North Korea of reneging on a 1994 accord by launching a secret atomic weapons program.

WAR.WIRE