The United States says the nuclear test threatened by North Korea would be a reckless and provocative act. Ambassador to the United Nations John Bolton says the matter will be raised in the Security Council.
U.S. officials believe Pyongyang has possessed at least a small number of nuclear weapons for more than a decade, but an actual test would greatly raise the stakes in international diplomacy over the North Korean program.
Traveling with Secretary of State Condoleezza Rice in Cairo, State Department spokesman Sean McCormack said a nuclear test by North Korea would pose an unacceptable threat to peace and stability in Asia and the world.
He said that such a provocative step would further isolate the reclusive communist state, and the United States will work with its allies and partners to discourage such a reckless action and will respond appropriately.
McCormack said a test would severely undermine U.S. confidence in North Korea's commitment to the Chinese-sponsored six-party talks, in which Pyongyang has been offered aid and security guarantees for giving up its nuclear program.
North Korea agreed in principle to accept such a deal in September of last year, but it has not returned to the six-party talks since a brief session in Beijing last November.
The North Korean government says it is boycotting the talks because of U.S. sanctions imposed last year against a Macao-based Chinese bank, Banco Delta Asia, that had been one of Pyongyang's main financial outlets to the rest of the world.
The Bush administration says the penalties were intended to counter North Korean money-laundering and counterfeiting of U.S. currency. U.S. spokesmen have said the issue is unrelated to the nuclear talks, but that the United States is prepared to discuss the matter with Pyongyang if it returns to the six-party forum.
North Korea said in its statement Tuesday that, what it called U.S. threats of war, and sanctions compelled it to conduct a nuclear test, and said that without a reliable deterrent its sovereignty was bound to be impinged on.
In July, North Korea conducted a salvo of missile tests including a failed launch of an intercontinental-range missile that ended a self-imposed moratorium on long-range testing.
A subsequent resolution in the U.N. Security Council condemned the tests and called for U.N. member countries to bar trade with North Korea that could support its missile program or unconventional weapons efforts.
There have been numerous reports, quoting U.S. and South Korean intelligence sources in recent years of possible North Korean preparations for an underground nuclear test.
U.S. experts believe Pyongyang may have possessed a few nuclear weapons since the late 1990s, but gained enough fissionable material to build several more devices after it expelled U.N. inspectors from its Yongbyong reactor complex in late 2002 and began extracting plutonium from spent fuel rods.