WASHINGTON - THE United States warned on Thursday that it will 'rethink' its approach to North Korean nuclear disarmament after the latest round of six-country negotiations collapsed in Beijing.

White House spokesman Dana Perino blamed the secretive Stalinist regime for scuttling the talks by refusing to accept a formal mechanism for verifying its statements about the extent of its atomic activities.

'Because they decided not to work with us, and the talks have devolved because they wouldn't put it in writing, we're going to have to rethink some of this action-for-action, which is what we had said we would do,' she said.

Ms Perino referred to a landmark six-nation deal in February 2007 that promised diplomatic and economic incentives - including energy aid - to North Korea in return for giving up the nuclear programmes it spent decades developing.

US State Department spokesman Sean McCormack said that the next heavy fuel oil shipment to North Korea, which had been set to come from Russia, was now 'under review' because of Pyongyang's rejection of a verification protocol.

Earlier, chief US envoy Christopher Hill departed Beijing after four days of talks, blaming Pyongyang for refusing to agree on a protocol to verify a historic declaration it made in June about its nuclear activities.

The six countries in the negotiations - North and South Korea, China, Japan, Russia and the United States - had sought to formalize a verification mechanism agreed to in principle, verbally, in October.

'The idea was to put all of this on a piece of paper so that everybody could understand what had been agreed to in the verification discussions,' and North Korea refused, Mr McCormack told reporters.

So 'all the parties said, 'OK, let's adjourn the meeting, go back to capitals, think about it, and we'll keep working this process',' Mr McCormack said, adding that 'North Korea on this question is isolated'.

North Korea's stance on the sampling of material to be taken away for analysis was a sticking point, Mr McCormack said.

The material 'covered not just plutonium, but HEU (highly enriched uranium) and proliferation activity,' he said.

With no date set for more talks, the deadlock this week all but dashed US President George W. Bush's hopes to make progress on North Korean disarmament before Mr Barack Obama moves into the White House on January 20.

'What's unfortunate is that the North Koreans had an opportunity here, there was an open door and all they had to do was walk through it because five of the members of the six-party talks had all agreed on a verification protocol,' said Ms Perino.

The negotiations have suffered countless setbacks since they began in 2003 and did not stop Pyongyang from testing its first atomic bomb in 2006.

Ms Perino indicated that it was unlikely Washington might backtrack on taking Pyongyang off a US terrorism blacklist, but warned that 'one of the things people think about is energy assistance'.

Hours later, Mr McCormack said in statement that while 'Russia was scheduled to deliver the next shipment of heavy fuel oil to the DPRK (North Korea)', it was now 'under review' because of North Korea's actions in Beijing.

Ms Perino said the next step was for Hill to report on the faltered discussions and that 'we'll keep you updated on next steps'.

Another White House official said privately that North Korean leaders may be calculating that they may get a better deal once Mr Obama takes office, but added: 'I think they're miscalculating.' -- AFP