North Korea nuclear test: Hydrogen bomb 'missile-ready'
North Korea says it has successfully tested a nuclear weapon that could be loaded onto a long-range missile.
The secretive communist state said its sixth nuclear test was a "perfect success", hours after seismologists had detected an earth tremor.
Pyongyang said it had tested a hydrogen bomb - a device many times more powerful than an atomic bomb.
Analysts say the claims should be treated with caution, but its nuclear capability is clearly advancing.
North Korea last carried out a nuclear test in September 2016. It has defied UN sanctions and international pressure to develop nuclear weapons and to test missiles which could potentially reach the mainland US.
South Korean officials said the latest test took place in Kilju County, where the North's Punggye-ri nuclear test site is situated.
The "artificial quake" was 9.8 times more powerful than the tremor from the North's fifth test, the state weather agency said.
It came hours after Pyongyang said it had miniaturised a hydrogen bomb for use on a long-range missile, and North Korean leader Kim Jong-un was pictured with what state media said was a new type of hydrogen bomb. State media said the device could be loaded on to a ballistic missile.
A series of recent missile tests has caused growing international unease.
In a report on Sunday, the North's state news agency KCNA said Kim Jong-un had visited scientists at the nuclear weapons institute and "guided the work for nuclear weaponisation".
The North has previously claimed to have miniaturised a nuclear weapon, but experts have cast doubt on this. There is also scepticism about the North's claims to have developed a hydrogen bomb.
However, this does appears to be the biggest and most successful nuclear test by North Korea to
date - and the messaging is clear. North Korea wants to demonstrate it knows what makes a credible nuclear warhead.
Hydrogen bombs use fusion the merging of atoms - to unleash huge amounts of energy, whereas atomic bombs use nuclear fission, or the splitting of atoms.
South Korean President Moon Jae-in said North Korea's sixth nuclear test should be met with the "strongest possible" response, including new United Nations Security Council sanctions to "completely isolate" the country.
China, North Korea's only major ally, condemned the test.
North Korea "has ignored the international community's widespread opposition, again carrying out a nuclear test. China's government expresses resolute opposition and strong condemnation toward this," the foreign ministry said in a statement.
Japan's Chief Cabinet Secretary Yoshihide Suga said sanctions against North Korea should include restrictions on the trade of oil products.
Russia meanwhile said the test defied international law and urged all sides involved to hold talks, saying this was the only way to resolve the Korean peninsula's problems.
The head of the International Atomic Energy Agency, the global nuclear watchdog, described the test as "an extremely regrettable act".
Yukiya Amano added: "This new test, which follows the two tests last year and is the sixth since 2006, is in complete disregard of the repeated demands of the international community."
The first suggestion that this was to be a far from normal Sunday in the region came when seismologists' equipment started picking up readings of an earth tremor in the area where North Korea has conducted nuclear tests before.
Initial reports from the US Geological Survey put the tremor at 5.6 magnitude with a depth of 10km but this was later upgraded to 6.3 magnitude at 0km.