The United States has warned North Korea of "severe consequences" to the diplomatic effort to end its nuclear programs if Pyongyang conducts a second atomic test.
The US State Department issued the warning as US and South Korean officials sought to play down reports that North Korea, which carried out its first nuclear test on October 9th, might be preparing for another.
South Korean officials said activity had been spotted near a suspected nuclear test site in North Korea but there was no evidence to suggest Pyongyang was about to test again.
"We do not have any indication that that kind of test is imminent," South Korean Foreign Minister Song Min-soon told reporters after meeting US Secretary of State Condoleezza Rice.
"The North Koreans would have to know that any such test would obviously further deepen their isolation," Ms Rice said.
US officials held out the possibility of a quick resumption of six-party talks on ending North Korea's nuclear ambitions if Pyongyang were to return to the table prepared to carry out its agreement to abandon its nuclear programs.
The talks, which involve the two Koreas, China, Japan, Russia and the United States, made no visible headway during their last round in Beijing in December.
State Department spokesman Sean McCormack said there were signs that a fresh round was possible this month but he made clear that a new North Korean nuclear test would be unwelcome.
"If you did have another test of a nuclear device, that would have severe consequences for the viability of that political-diplomatic process - why would they take such a step at this time?" State Department spokesman Sean McCormack told reporters.
The talks were designed to find a way to carry out a six-party agreement reached on September 19th, 2005 in which North Korea said it was committed "to abandoning all nuclear weapons and existing nuclear programs." In return, the other countries held out economic, political and security incentives.
Despite the failure of the last round, Ms Rice said the parties had made some progress. "One of the reasons that you are hearing some sense that we might be able to return sooner than later is that when you look at what happened in the last round of the talks, there actually was significant groundwork laid for potential outcomes that could be useful," She told a news conference.
"If there are signals that in fact the North is now ready to come back in a more constructive way ... I do think that we could be back in talks fairly soon," she added, but declined to say when that might be.