The United States told North Korea on Wednesday that the world would consider a nuclear test by the nation a "deeply provocative act."
State Department spokesman Sean McCormack also urged nations, including Pyongyang's ally China, "to state very clearly to North Korea that this would be a very provocative act and it would only add to and deepen their isolation."
His comments come amid worry that North Korea might soon test a nuclear bomb. South Korea's main spy agency warned last week that Pyongyang could test a nuclear device at any time. McCormack would not comment specifically about reports of a possible test.
China, seen as North Korea's last major ally, and four other nations are working to persuade North Korea to scrap its self-declared nuclear weapons production program.
Negotiations have been stalled since November, however, with the North demanding that the United States lift financial restrictions imposed for alleged financial wrongdoing, including what Washington says is state-sponsored counterfeiting of U.S. currency.
Last month, the North defied repeated international warnings and test-fired seven missiles, prompting China to join in a U.N. Security Council resolution condemning the tests.
McCormack said of the U.S. financial restrictions that "North Korea has earned its way to this position the honest way: through their misbehavior and through their actions."
"It's pretty simple," he said. "Don't engage in counterfeiting, don't engage in illicit behavior and you won't have these kinds of problems."
Secretary of State Condoleezza Rice was set to meet Wednesday with South Korea's national security adviser for talks on South Korean President Roh Moo-hyun's visit next week to Washington McCormack said.