After weeks of intensifying warnings from Washington and threats by Pyongyang, US policymakers are hoping to stop the crisis from spiraling into war while still standing firm on North Korea.

North Korea is famous for its shrill proclamations but it has sent shudders in the United States, South Korea and Japan in recent days by brandishing nuclear war and apparently moving a missile to its east coast.

The United States took the unprecedented step of announcing last week a bomb test by its nuclear-capable B-2 stealth fighter, one of a series of moves meant partly as reassurance to the new administration in ally South Korea.

A senior US official insisted that such shows of force were needed to influence North Korea but said that the United States also wanted to climb down from the crisis and minimize the potential for a miscalculation.