North Korea declares that it has carried out a test of a nuclear bomb after the detonation was detected by the U.S. Geological Survey.
The explosion was registered as a 5.1-magnitude seismic event by the USGS shortly before 10 p.m. Monday night.
The U.S. Office of the Director of National Intelligence said in a statement that it had assessed that North Korea "probably conducted an underground nuclear explosion in the vicinity of P'unggyethe" with a yield of "several kilotons."
In a statement, President Barack Obama described the test as a "highly provocative act."
Obama said, "North Korea's nuclear weapons and ballistic missile programs constitute a threat to U.S. national security and to international peace and security."
Obama also said, "The United States remains vigilant in the face of North Korean provocations and steadfast in our defense commitments to allies in the region."
Meanwhile, the test prompted the U.N. Security Council to call for an emergency meeting Tuesday afternoon.