North Korean state media reported Saturday that the reclusive nation had successfully tested an engine for an intercontinental ballistic missile.
The Korean Central News Agency said North Korean leader Kim Jong Un had personally supervised the test, which it said would strengthen the country's ability to stage nuclear strikes against the United States.
Pyongyang has repeatedly threatened pre-emptive nuclear strikes on the United States and South Korea. Saturday's engine test, if successful, would be a big step forward for the North's nuclear weapons program.
North Korea has conducted a series of apparent weapons tests since January and has test-fired missiles in defiance of sanctions against such tests imposed by the U.N. Security Council.
South Korean and U.S. analysts have questioned the North's claims that the tests demonstrated significant technological advances in its missile and nuclear programs.