"We've made no decisions at this point, other than just to say we are prepared for a bilateral talk, if that will help advance the six-party process."

'Major concession'

He denied the move marked a significant change in policy, saying any bilateral meeting would be aimed at bringing Pyongyang back to multilateral talks.

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But John Harrison, a professor at the S Rajaratnam School of International Studies in Singapore, told Al Jazeera the move was a significant step by the US.

"One of the biggest things North Korea has wanted throughout this [six-party] process is direct discussions with the United States.

"And the United States's position has always been that this is an international issue, one that's dealing with regional security and there should be regional partners.

"So this concession is fairly major."

Crowley said it was unlikely that any bilateral talks would take place before the UN General Assembly, to be held in New York later this month, and he declined to say whether Stephen Bosworth, the US special envoy, might accept the North's invitation to visit Pyongyang.

For his part, Bosworth gave no hint of a change in plan when he spoke in Tokyo last week.

Six-party partner South Korea said that direct talks between Pyonyang and Washington were welcome as a move to advance the stalled negotiation process.

"South Korea will not oppose US-North Korea bilateral talks if they are held to advance the six-party talks to resolve the North Korea nuclear issue," Moon Tae-young, a South Korean foreign ministry spokesman, said.

Nuclear tests

Talks on Pyonyang's nuclear programme have unfolded in fits and starts, with North Korea taking some steps to disable its nuclear facilities after agreeing an aid-for-disarmament deal in September 2005.

However, it has carried two nuclear tests since, first in 2006 and then in May this year.

Despite condemnation from the UN Security Council over its nuclear testing, the North followed the test in May with several missile tests, ratcheting up tension with Japan and South Korea.

Recently, Pyonyang has softened its posture and sought bilateral talks with Washington, while still trying to have the six-party negotiations scrapped.

Pyongyang said last week it had reached the final stages of enriching uranium and was also building more plutonium-based atomic weapons.