Verification of the kind of device North Korea tested - specifically, whether it was a fully staged thermonuclear bomb - would require the collection of radionuclides released by the detonation into the atmosphere.
North Korea's news agency also reported that the bomb was created to be fitted onto an intercontinental ballistic missile.
Slamming Pyongyang for ignoring global condemnation of its atomic weapons programme. "It also underlines yet again the urgent need for the global community to act on putting in place a legally binding ban on nuclear testing once and for all".
It was not immediately known whether the nuclear device apparently set Sunday was an H-bomb.
He said the government registered a protest with the North Korean embassy in Beijing prior to the confirmation, calling any test "extremely unforgivable".
The test came just hours before Chinese President Xi Jinping was scheduled to open a summit of BRICs nations in southern China.
"Though we cannot verify the claim, (North Korea) wants us to believe that it can launch a thermonuclear strike now if it is attacked".
But the rapid progress of North Korea's missile technology, its attainment of an intercontinental ballistic missile, and the latest nuclear test now have many analysts saying negotiations may need to begin with an acceptance of North Korea as a nuclear state.
Japanese Foreign Minister Taro Kono said they had examined the data from the tremors and "concluded that it was a nuclear test", while Mr Abe said Japan was speaking to other nations. The US Geological Survey called the first quake an explosion with a magnitude 6.3.
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At the time Fagen told music magazine Billboard: " Walter's recovering from a procedure and hopefully he'll be fine very soon". He encountered his future partner Fagen as a student at Bard College in NY while playing a gig at local club the Red Balloon.
The White House said Trump's national security team was "monitoring this closely" and that the president would convene a meeting of his advisers later on Sunday.
Earlier, the Japan Meteorological Agency had observed a magnitude-6.1 tremor in North Korea, which showed a different waveform from a natural quake.
North Korea conducted two nuclear tests last year, the last almost a year ago, on the September 9 anniversary of the nation's founding. It has since maintained a torrid pace inweapons tests, including its first two inter continental ballistic missiles test in July.
U.S. President Donald Trump admonished South Korea, a key ally, for what he termed a policy of "appeasement" after North Korea claimed to have tested an advanced hydrogen bomb for a long-range missile on Sunday.
In its report, KCNA (via Xinhua, China's official news agency) also said the North Korean leader "guided the work for nuclear weaponization on the spot", as part of "the final-stage research and development for perfecting the state nuclear force".
"I think at some point the American president, and I'm not inside so don't know what he's being told about how long he has, but at some point if you're threatening Guam and already firing missiles over Japan, we're getting pretty close to a denouement, we're getting pretty close to a president having to make a decision", Rice said, referring to the country's recent threats to fire missiles off the coast of Guam, a USA territory in the Pacific.
It may be hard for outside experts to confirm that the nuclear device detonated on Sunday was an H-bomb.
The move comes after weeks of aggression from North Korea toward the US and its allies.
To back up its claims to nuclear mastery, such tests are vital.