Alarm after North Korea claims it tested H-bomb
Claims by North Korea that it conducted a hydrogen bomb test have been met by worldwide condemnation.
The secretive state said it successfully tested a miniaturised hydrogen bomb, a move which would be a significant advancement of its nuclear armoury.
Last night the UN said that it was drafting further sanctions against Pyongyang.
Leader Kim Jong-un's test has prompted an international outcry and the incident has even been condemned by China, the regime's main ally.
But there is already widespread scepticism as to whether the bomb - which created a 5.2 magnitude earthquake when it was tested - is truly a thermonuclear device.
Whereas atomic bombs such as those already tested by North Korea in 2003 and 2009 are powerful weapons, they are nowhere near as devastating as hydrogen bombs.
But this has not stopped the international community from being gripped with alarm over the test, which shows North Korea is another step closer to becoming one of the leading nuclear threats on earth.
Japan has already dispatched H4 training planes to investigate whether the test has unleashed nuclear material in the atmosphere, though initial reports say this is unlikely.
Meanwhile, in Pyongyang, North Koreans were seen "celebrating" the launch as they gathered around TV screens at the capital's rail station.
Several experts have already warned of complacency over Kim Jong-un's actions, with one former British ambassador to the regime urging against assuming he does not have the resolve to launch a nuclear strike.
US House Speaker Paul Ryan said the test appeared to be a "provocation". But he added that it was too soon to push for a US response until the facts of the incident are known.
"I think this means we have to have a well-honed response with our allies on this rogue regime," Ryan told reporters after a meeting of his Republican Party. "We don't know that he facts yet," he said, adding: "This looks like a provocation."
North Korean state media said: "The (country's) access to H-bomb of justice, standing against the US, the chieftain of aggression...is the legitimate right of a sovereign state for self-defence and a very just step no-one can slander."
The test, the state's first since 2013, came as a surprise to many, as no mention of it had been made in Kim Jong-un's New Year speech.
Experts believe the bomb will largely be used as a means of increasing North Korea's influence on the world stage.
But the magnitude of the earthquake following the explosion was not consistent with what would be expected from such a blast, critics said.
The US Geological Survey measured an earthquake with a magnitude of 5.1 - bigger than the three previous bombs in 2013, 2009 and 2006.
But the explosive yield is only a fraction of what would be expected during the explosion of a hydrogen bomb, it is claimed.
South Korean politician Lee Cheol Woo said he had been briefed by the country's National Intelligence Service and was told even a failed H-bomb detonation would have a higher explosive yield than was registered.
Chemical weapons analyst Karl Dewey suggested it was more likely the blast was caused by a boosted fissure weapon.
He said: "Hydrogen bombs use lithium deuteride and it is not known if North Korea has the infrastructure to create such material.
"What may be more plausible is the development of what is known as a boosted fission weapon. Simple fission weapons or boosted weapons can be used to set off a thermonuclear secondary, but shouldn't be confused with them."