Katty Kay BBC correspondent in Washington

Washington joined Beijing in condemning North Korea's surprise decision to pull out of the nuclear Non-Proliferation Treaty.

President George W Bush and President Jiang Zemin spoke by telephone to discuss the situation shortly after North Korea's announcement and described the move as cause for concern.

Meanwhile Pyongyang's Ambassador to the United Nations, Pak Gil-yon, warned on Friday that any decision to impose UN sanctions on North Korea would be a "declaration of war."

The United States was eager to repeat its assertion to North Korea that it has no hostile intentions to the closed communist country.

Pyongyang expelled nuclear inspectors last week

But Washington's determination to downplay the severity of the North Korean nuclear situation is being thoroughly tested by these latest developments.

"The President said that this - the Non-Proliferation Treaty - binds us in a common purpose.

"The President stressed that the United States has no hostile intentions toward North Korea, and sought a peaceful, multilateral solution to the problem created by Pyongyang's action," said White House spokesman Ari Fleischer.

Implications unclear

The implications of Pyongyang's decision to pull out of the international treaty were not immediately clear.

It does mean that in 90 days North Korea will no longer be bound by the terms of the agreement.

But a government statement said North Korea had no intention of producing nuclear weapons. The statement said the decision to withdraw was motivated by the need for self defence in the face of US threats.

"Though we pull out of the NPT, we have no intention to produce nuclear weapons and our nuclear activities at this stage will be confined only to peaceful purposes such as the production of electricity," the statement said.

The United Nations nuclear monitoring agency urged North Korea to reverse its decision and said it was important to defuse the crisis.

It said North Korea must take the first step in compliance but should be offered rewards for good behaviour.

The situation has deteriorated since October last year when the US said North Korea admitted to pursuing a nuclear arms programme.

From Washington's point of view the North Korean situation comes at a very bad time.

The White House wants to remain focused on its operations against Iraq and sees North Korea as an unwelcome distraction. President Bush's differing responses to Baghdad and Pyongyang has opened him up to accusations of inconsistency.