What 'hydrogen bomb' test means for N Korea nuclear aims

North Korea says it has for the first time successfully tested a hydrogen bomb.

The announcement was made on state television, hours after a tremor with a magnitude of 5.1 was detected near a known nuclear test site.

But South Korea's deputy defence minister said it was difficult to believe the device was a hydrogen bomb.

Jonathan Marcus assesses North Korea's nuclear capabilities in light of the latest test claims.

Video produced by James Reevell