North Korea, which declared on October 9 it had tested its first atomic bomb, has long sought one-on-one talks with US President George W. Bush's administration.
Bush administration officials have repeatedly met one-on-one with North Korea, but only on the sidelines of six-nation talks, which started in 2003.
"We ask them to come back to the six-party talks to engage in discussion," Thomas Schieffer, the US ambassador to Japan, told reporters.
"We are happy to discuss the issues with them in a bilateral way, or in a multilateral system, if they would come back to those talks. So if they want to resolve and defuse this crisis there's ample opportunity to do that. And we hope they take advantage of that," he said.
North Korea stormed out of the talks -- which also included China, Japan, Russia and South Korea -- in November last year, to protest US sanctions on a Macau bank accused of laundering and counterfeiting money for Pyongyang.
Just two months before the boycott, North Korea agreed in general terms, at the fifth and last round of six-way talks, to give up its nuclear weapons program in exchange for aid and security guarantees.
Schieffer appealed to North Korea not to test another nuclear bomb, saying it would be "another provocative step".
Chinese officials said Tuesday North Korean leader Kim Jong-Il had told a Chinese envoy he had no plans for a second nuclear explosion. But Schieffer said North Korea's intentions remained unclear.
"I don't think any of us knows whether North Korea is about to explode another nuclear device and I suspect that, if indeed they did, we would not know about it until pretty shortly before they did it, because so much of this sort of stuff is done underground," Schieffer said.

Copyright AFP (Agence France-Presse), 2006