"We are confident ... that of course the United States and its allies can deal with any potential threat from North Korea," Secretary of State Condoleezza Rice said in Luxembourg at the tail end of her European tour.

"And North Korea I think understands that," the chief US diplomat said, following an official statement from Pyongyang that it had developed nuclear weapons to protect itself against a US attack and would indefinitely boycott six-party talks aimed at dismantling its atomic program.

Rice said North Korea only faced deeper isolation if it continued on its present path, adding "the world has given them a way out and they should take that way out."

Some analysts say the North Korean move was aimed at extracting concessions from Washington before any reconvening of the nuclear talks among the United States, two Koreas, Japan, Russia and China.

North Korea attended three rounds of the talks but shunned a fourth round set for last September, complaining of "hostile" US policies.

The White House and State Department indicated separately Thursday that the United States does not plan to sweeten a deal introduced at the third round in June in return for North Korea to end its nuclear arms program.

This came despite persistent reports that China and South Korea particularly wanted more concessions for Pyongyang.

"Our position is consistent, and we don't see a need to review it," said deputy State Department spokesman Adam Ereli at a media briefing.

"We've got a proposal on the table. We think it's a good proposal. We think it goes in a positive direction in addressing mutual concerns."

But, later noting a "common concern" despite "differences" between the nuclear situation of North Korea compared to Iran, Ereli added: "We are working in both cases to offer a wiser, more responsible alternative that we believe it's in the interest of everybody to choose.

"We have said that force is not an option at the moment and that we are committed to pursuing this solution diplomatically.

"We have said very clearly that a peaceful diplomatic solution is our preferred option or preferred course and the one to which we are working with full conviction," Ereli said.

White House spokesman Scott McClellan said the US proposal "addresses the concerns of all parties."

He said North Korea should return to the six-party talks and "discuss how we can move forward on the proposal that is on the table."

At the June meeting, the United States proposed multilateral security guarantees and energy aid by China, Russia, South Korea and Japan to North Korea in return for highly intrusive inspections and an agreement for complete dismantling of all of its nuclear facilities.

The North Koreans have never responded to that proposal.

South Korean Foreign Minister Ban Ki-Moon arrived in Washington Thursday for talks with US officials as part of fresh high-level efforts to contain the nuclear crisis in the Korean peninsula.

Ban met US senators Thursday, and is due to meet Vice President Dick Cheney on Friday and Rice on Monday ahead of separate talks between US diplomats and defence officials with their Japanese counterparts on February 19.

US Defence Secretary Donald Rumsfeld on Thursday voiced concern over the latest North Korean threat.

Pyongyang's "dictatorial regime" was a threat in terms of proliferation but also to its own people, he said on the sidelines of a meeting of NATO defence ministers in Nice, France.

"Given their dictatorial regime and the repression of their own people, one has to worry about weapons of that power in the hands of leadership of that nature," he said.

Rumsfeld said he could not say for sure whether Pyongyang has a bomb or the ability to make one, and underlined the difficulty of taking Pyongyang's claims at face value.

The CIA said last year that judging its activities in the mid-1990s, North Korea had produced one, possibly two, nuclear weapons and that the pool of 8,000 nuclear spent fuel rods the North claimed to have processed into plutonium metal would provide enough plutonium for several more.

It also believed Pyongyang was pursuing a production-scale uranium enrichment program based on technology provided by Pakistani scientist Abdul Qadeer Khan's illicit network, which would give it an alternative route to nuclear weapons.