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.

Hours before the seismic activity, South Korean media reported that Pyongyang had test-fired a ballistic missile from a submarine in late December. It is unclear whether the test was successful or not.

In May last year, North Korea claimed it had successfully launched a missile from a submarine.

Strong reaction started pouring in after the North Korean announcement of the hydrogen bomb test, with South Korea saying it was a serious challenge to global peace and a violation of UN Security Council resolutions.

The Japanese Prime Minister Shinzo Abe said it was a threat to Japan’s safety and could not be tolerated.

The US called on North Korea to abide by its international commitments and obligations saying it would respond to provocations.

After previous tests, the international community has responded with economic and political sanctions.



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