In an emergency communication sent yesterday, Washington warned Beijing that Pyongyang was possibly planning a test nuclear explosion, an unidentified US official told the Journal.

The report comes after Pyongyang declared in February that it had nuclear weapons for self-defense.

The Journal reported that the US told China it "believes the North Korean nuclear program is advanced enough that a test could come with little or no warning."

"It's clear the North Koreans want the world to think that they are moving quickly and rapidly toward a nuclear test," the official told the Journal.

The official said that US spy satellites have detected increased activities at North Korean sites where underground nuclear tests could be carried out.

The US State Department said it was "following closely all information about activities in North Korea" but declined specific comment on the reported planned nuclear test.

"Consistent with longstanding policy however we do not comment on reports about intelligence matters," department spokeswoman Darla Jordan told AFP.

The department does not have any "new assessment" to offer regarding North Korea's nuclear weapons program, she said.

"We remain in regular close contact with our partners in the six-party talks on how to resolve our shared concerns about North Korea's pursuit of nuclear weapons," Jordan said.

The Journal quoted the official as saying that the true intent of the increased activities at North Korean sites where underground nuclear tests could be carried out was difficult to ascertain.

Another official told the newspaper that similar warnings were being sent to South Korea and Japan.

According to reports earlier this week, North Korea recently shut down its only functioning nuclear reactor and told a visiting US specialist that it planned to unload spent nuclear fuel from the plant and reprocess it into weapons-grade plutonium.

Two years ago, North Korea said it reprocessed enough spent fuel from the reactor to produce plutonium for six to eight atom bombs.

US intelligence believes the country could already possess one or two crude nuclear bombs based on fuel reprocessed in previous decades.

Six-party talks between the Pyongyang regime and the US, South Korea, China, Russia, and Japan aimed at ending North Korea's nuclear arms ambitions stalled last year after three inconclusive rounds.

The United States has been concerned about recent "provocative North Korean statements and have shared these concerns with our partners in the six-party process," State Department spokeswoman Jordan said.

"We continue to believe such statements do nothing to bring this issue to a resolution. On the contrary, they serve only to further isolate the north," she said.

North Korea has repeatedly said that it planned to build more atomic bombs after declaring itself a nuclear-armed state in February.

The United States has been trying to use China's influence to rein in North Korea but have been unable to get the hardline regime to the negotiating table.

Secretary of State Condoleezza Rice said this week that US forces present a "significant deterrent" against any nuclear threat from Pyongyang, and she may yet seek UN Security Council sanctions against it.

"Now we reserve the right and the possibility of going to the Security Council, should it be necessary, of putting other measures in place, should it be necessary," she said.

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