North Korea announces H-bomb test
The North Korean authorities say they have successfully tested a hydrogen bomb amid reports of a tremor near the main nuclear test site.
State media announced the test after monitors detected a 5.1 magnitude quake close to the Punggye-ri site.
The North is thought to have conducted three previous underground nuclear tests there since 2006.
A hydrogen bomb uses fusion to create a blast far more powerful than that of a more basic atomic bomb.