"This is not helpful. It does not serve North Korea's interests and the interest of peace and stability in the region," said a State Department official, who asked not to be named.

North Korea, which is boycotting six-party talks on its nuclear arms program, announced Thursday it was ending a moratorium on testing long-range missiles that it declared in 1999.

A statement by the official Korean Central News Agency (KCNA) also said that a "hostile" US policy was forcing it to develop its nuclear arsenal.

The US official was at a loss to explain the significance of the latest pronouncements from Pyongyang and whether they represented an escalated threat. But he said "it only increases their isolation."

"It is certainly not conducive to getting us back to the six-party talks," he said, referring to the negotiations that also included China, Japan, South Korea and Russia.

The discussions aimed at persuading North Korea to renounce its nuclear ambitions broke off in September, and Pyongyang has issued a series of bellicose statements in recent weeks.

The State Department official would not speculate on how long the United States and its allies could wait before taking other measures to end North Korea's nuclear threat.

He said Washington was committed for the moment to a diplomatic solution through the six-party talks, but added that "somewhere along the way people might decide that there's a need to change the policy."

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