Why is North Korea forging ahead with a nuclear programme?
Its leadership says it's a necessary self-defence measure against a potential attack by arch enemy the United States.
It's the country's first hydrogen-bomb test and considered by analysts as an unanticipated advance in its limited nuclear arsenal.
How does a hydrogen bomb differ from an atomic bomb?
Atomic bombs rely on fission, or atom-splitting, just as nuclear power plants do. The hydrogen bomb, also called the thermonuclear bomb, uses fusion, or atomic nuclei coming together, to produce explosive energy.
What would a successful H-bomb test mean to North Korea?
It would be a big advance in the country's nuclear weapons programme. North Korea is thought to have a handful of rudimentary nuclear bombs and has spent decades trying to perfect a warhead small enough to place on a missile that can reach the US.
Why is there scepticism about the North Korean H-bomb test claims?
South Korea's spy agency thinks the estimated explosive yield from the blast was much smaller than what even a failed hydrogen bomb detonation would produce. The White House says early analysis of underground activity "is not consistent" with the North's claim of a successful H-bomb test.
Some analysts say the North probably hasn't achieved the technology needed to make a miniaturised warhead that could fit on a long-range missile capable of hitting the US.
What would a confirmed test mean to the region?
It would further worsen already abysmal relations between Pyongyang and neighbouring countries including South Korea, Japan and sour links with ally China. It's also expected to lead to a strong push for tougher sanctions by the United Nations against the already impoverished nation.