North Korea claims it has conducted powerful H-Bomb test

North Korea said it had conducted a powerful hydrogen bomb test, a defiant and surprising move that, if confirmed, would be a huge jump in Pyongyang's quest to improve its nuclear arsenal.

A television anchor said the North had tested a 'miniaturised' hydrogen bomb, in a 'perfect success', elevating the country's 'nuclear might to the next level' and providing it with a weapon to defend against the US and its other enemies.

South Korea's defence ministry said that it was bolstering its security posture in response.

There has long been scepticism by Washington and nuclear experts on past North Korean claims about H-bombs, which are much more powerful, and much more difficult to make, than atomic bombs.

But a confirmed test would be seen as extremely worrying and lead to a strong push for new, tougher sanctions on North Korea at the United Nations. The UN Security Council has tentatively scheduled an emergency meeting.

It would also further worsen already abysmal relations between Pyongyang and its neighbours.

North Korean nuclear tests are worrying because each new blast is seen as pushing North Korea's scientists and engineers closer to their goal of building a bomb small enough to place on a missile that can reach the US mainland.

A successful H-bomb test would be a big step for the North. In a hydrogen bomb, radiation from a nuclear fission explosion sets off a fusion reaction responsible for a powerful blast and radioactivity.