The US on Friday denied it had made a significant shift on North Korea policy by contemplating a sequence of inducements for the Stalinist state to renounce nuclear weapons.
The Bush administration previously insisted Pyongyang must verifiably dismantle its nuclear weapons production before it could expect benefits in return from the US.
A senior administration official indicated on Thursday that some unspecified US measures could be offered to Pyongyang before a final settlement was reached.
"It would not be correct to say that they would have to do everything, before they would hear anything," the official said.
The New York Times quoted other unnamed senior officials as saying that the US team at six-nation crisis talks in Beijing last week told North Korea that Washington could offer intermediate measures like food and aid to reward a change of North Korean behavior.
US President George W. Bush has frequently warned he will not submit to what he sees as "blackmail" by buying off Pyongyang's weapons programs, a line which has been seen as precluding any step by step inducements from Washington.
White House spokesman Scott McClellan did not specifically rule out such an approach but said Friday that Pyongyang must act first.
"Nothing can happen until North Korea changes its behavior and begins to take concrete steps to dismantle its nuclear weapons program," McClellan said.
"North Korea must end, verifiably and irreversibly, its nuclear weapons program.
"There is a strong message going to North Korea. North Korea is learning that the international community is not going to reward bad behavior," he said.
US Department of State spokesman Richard Boucher added: "If North Korea is changing its behavior, then we're willing to talk about what's possible."
"But, at the same time, we don't intend to offer inducements or rewards for North Korea's developing nuclear weapons, contrary to all its previous understandings."
Boucher's boss, Secretary of State Colin Powell meanwhile said on Friday that Washington was looking at how it could satisfy Pyongyang's demand for security assurances, ahead of the next round of six party talks, the date for which is yet to be set.
"The only thing that North Korea has said to us that they would like to see from the United States is a security assurance that we are not planning to attack them or invade them," Powell said after meeting Mexican Foreign Secretary Luis Ernesto Derbez.
"We have said that and they wish to see this assurance provided in some form that they would have confidence in.
"That's the stage of discussion and negotiation we are at now ... we are looking at ways in which we can give them the kind of assurance that they say they need."
The US had refused to offer North Korea a formal non-aggression treaty as a price for ending the crisis.
But Powell has in the past suggested that some form of US statement that it has no plans to attack or invade North Korea could be noted in some way by Congress, short of a formal treaty ratification.
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