North Korea nuclear: State claims first hydrogen bomb test

North Korea says it has successfully carried out an underground hydrogen bomb test which, if confirmed, would be its fourth nuclear test since 2006.

This is North Korea's first claim to have tested a hydrogen bomb, which is more powerful than an atomic weapon.
International experts say there is no confirmation of this yet.
But the announcement was swiftly criticised by world leaders, with South Korea calling it "a grave provocation to our national security".