"You know, there are a lot of rumours about this, obviously there are some indications, but I would caution people not to put too much stock in that," Assistant US Secretary of State Christopher Hill told National Public Radio's Morning Edition.
"We have always felt that the North Koreans could conduct a test when wanted to but we do not have any indication that it's going to happen imminently," he said.
State Department spokesman Tom Casey said US officials were constantly in touch with the Chinese at many levels. "But we certainly haven't received any information from them, from the Chinese, that they've been told by Pyongyang that another test is imminent," he told reporters.
CNN said on Tuesday that a US intelligence analyst had told it the intelligence community had seen what might be preparations for a nuclear test at least three North Korea sites.
The activity at one site looks very similar to activity seen at the site of North Korea's October 9 nuclear test just before an explosion there, CNN said it was told.
Also on Tuesday, NBC reported that Beijing had been informed by Pyongyang of additional nuclear tests. But later a Chinese Foreign Ministry spokeswoman told CNN, "We have not received any notice from North Korea regarding this issue."
One US intelligence official said it was particularly difficult to predict a possible test as the North Koreans had only carried out one before and much of the activity would take place underground.
"We don't really have a baseline to compare," the official said.

Copyright Reuters, 2006