U.S. intelligence officials have confirmed that North Korea conducted an underground nuclear test last week.
A statement from the U.S. Director of National Intelligence says radioactive material detected in air samples confirms a nuclear explosion of less than one kiloton.
The announcement comes as Secretary of State Condoleezza Rice prepares to visit North Korea's neighbors for talks on implementing sanctions punishing North Korea and convincing the country to return to nuclear disarmament talks.
Speaking to reporters in Washington on Monday, Rice said she plans to meet with Japanese, South Korean and Chinese officials to discuss coordinating inspections of all cargo going into and out of North Korea.
Chinese officials said today that while troops will inspect cargo from North Korea for banned weapons materials, their forces will not stop and board North Korea ships.
China's U.N. ambassador, Wang Guangya had said earlier that his country opposes interdiction, which was an apparent reference to stopping ocean-going cargo.
U.S. intelligence officials say Monday's nuclear test released significantly less explosive force than North Korea had expected. Officials said intelligence indicated the North Koreans predicted an explosion the equivalent of four kilotons of high explosives -- but the test released less than one kiloton.