The White House was reacting to an ABC News report that the communist nation may be preparing for an underground test of a nuclear bomb.
ABC on Thursday quoted an unidentified senior State Department official as saying, "It is the view of the intelligence community that a test is a real possibility."
ABC also quoted an unidentified senior military official as saying that a U.S. intelligence agency recently had observed "suspicious vehicle movement" at a suspected North Korean test site. The activity involved the unloading of reels of cable outside an underground facility in northeast North Korea.
According to ABC, information about the cables, which can be used to link an underground test site to remote monitoring equipment, was brought to the attention of the White House last week.
White House officials declined to confirm the report.
Asked about the report, two U.S. officials said there was no evidence to suggest that an underground nuclear weapons test by North Korea was imminent. The officials spoke on condition of anonymity because of the classified nature of the subject.
The Japanese Defense Agency in Tokyo also said it had not received any information or reports about any such preparations or unusual activities.
The United States has been concerned for some time that Pyongyang would seek to conduct a nuclear test, particularly given its public statements about its nuclear ambitions.
Last year, the United States warned allies that North Korea might be ready to carry out an underground nuclear test. In April 2005, diplomats in Vienna, Austria, said information about a possible underground nuclear test came in part from satellite imagery.
An official, who declined to be identified, said the White House position was that a "North Korean nuclear test would be an extremely provocative action that would draw universal condemnation from the international community."
The United States has urged North Korea to return to stalled six-party talks involving the Koreas, Russia, China and Japan. The nuclear talks were last held in November, when negotiators made no progress toward implementing an agreement in which North Korea agreed to give up its nuclear program in exchange for aid and security guarantees.
North Korea has refused to return to the negotiations until Washington lifts financial restrictions it imposed on the communist regime for alleged illegal activity, such as counterfeiting. The United States says the North should return to the talks without conditions.
In early July, North Korea test-fired seven missiles, including a new long-range model believed capable of reaching the U.S. that failed shortly after takeoff. The move violated the country's self-imposed moratorium on long-range missile launches.
The launches prompted the U.N. Security Council to unanimously pass a resolution sanctioning the North, which Pyongyang has rejected as an infringement on its sovereign right to conduct missile launches.