The United States has warned it will not accept a nuclear-armed North Korea, and China is calling for calm amid signs that Pyongyang is preparing to stage a new long-range missile exercise.
US Defence Secretary Robert Gates told a security forum in Singapore that North Korea's actions, including an atomic bomb test last Monday, could spark an arms race with serious consequences for Asia.
A South Korean newspaper has reported the North Koreans are preparing to move an intercontinental ballistic missile from a factory near the capital to a launch site on the east coast.
Mr Gates said the Obama administration would hold North Korea "fully accountable" if it transferred any nuclear material outside its borders.
