North Korea nuclear: State claims first hydrogen bomb test

North Korea says it has successfully tested a miniaturised hydrogen bomb which, if confirmed, would be its fourth nuclear test since 2006.

It came after a 5.1 magnitude quake was detected close to its nuclear test site at Punggye-ri, indicating a test may have been conducted.

This is North Korea's first claim to have tested a hydrogen nuclear bomb - more powerful than an atomic bomb.

International experts have cast doubt over the North's nuclear capabilities.

Suspicion of an underground 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.

Then 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."

It could be days or weeks before independent tests are able to verify the claim.

Last month, North Korean leader Kim Jong-un said Pyongyang had developed a hydrogen bomb, although many experts were sceptical.

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.

What is a hydrogen bomb?

• A weapon where the nuclear fusion of hydrogen isotopes creates a rapid release of energy, developed in 1952 by the United States

• Also known as a thermonuclear bomb, it can be much more powerful than atomic weapons that use fission
• Such bombs can be as small as a few feet long and can fit in warheads of ballistic missiles

North Korea and nuclear weapons

October 2002: North Korea first acknowledges it has a secret nuclear weapons programme

October 2006: The first of three underground nuclear explosions is announced, at a test site called Punggye-ri

May 2009: A month after walking out of international talks on its nuclear programme, North Korea carries out its second underground nuclear test

February 2013: A third nuclear test takes place using what state media calls a "miniaturised and lighter nuclear device"

May 2015: Pyongyang claims to have tested a submarine-launched missile, which are more difficult to detect than conventional devices

January 2016: North Korea says it has successfully tested a hydrogen bomb