North Korea announces hydrogen bomb test
15 minutes ago
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.
If confirmed, it would mean Pyongyang is intent on pursuing its nuclear programme with little regard for the major political and diplomatic costs that will inevitably accompany this unwelcome development, says Dr John Nilsson-Wright of Asia Programme at Chatham House.
In a surprise announcement a newsreader on North Korean state TV said: "The republic's first hydrogen bomb test has been successfully performed at 10:00 am on January 6, 2016."
Last month, North Korean leader Kim Jong-un said Pyongyang had developed a hydrogen bomb, although international experts were sceptical.
What is a hydrogen bomb?
A weapon energised by the nuclear fusion of hydrogen isotopes in a chain reaction, developed in 1958 by the United States
Also known as a thermo-nuclear bomb, it is seen as a "cleaner" bomb than an atomic one as it has less radioactive fallout - but also much more powerful
Unlike an atomic bomb, powered by nuclear fission, a hydrogen bomb is powered by the fusion of lighter elements into heavier elements
Such bombs can be as small as a few feet long and can fit in warheads of ballistic missiles
Suspicion of a test was first raised after the US Geological Survey said the epicentre of the quake - detected at 10:00 Pyongyang time (01:30 GMT) was in the north-east of the country, some 50km (30 miles) from Kilju city, near Punggye-ri.
The BBC's Kevin Kim in Seoul says analysts will now focus on trying to detect if any gases have leaked from the subterranean explosion to conclude what type of nuclear material may have been used, if it indeed it was a test of a hydrogen bomb.