North Korea "has ignored the worldwide community's widespread opposition, again carrying out a nuclear test".
North Korea's regime has "succeeded in making a more developed nuke", according to state news agency KCNA.
Aside from the factuality of the North's claim, the language in its statement seems a strong signal that Pyongyang will soon conduct another nuclear weapon test, which is crucial if North Korean scientists are to fulfill the national goal of an arsenal of viable nuclear ICBMs that can reach the United States (US) mainland.
Sunday's test comes after North Korea carried out its most provocative ballistic missile test to date; it flew a Hwasong-12 intermediate-range ballistic missile (IRBM) over Japanese territory into the northern Pacific Ocean, in a first, last week. North Korea's fifth nuclear test, in 2016, was also conducted soon after the joint U.S. military drill that North Korea has strongly protested is a threat to its security.
The co-ordinates of the two quakes were nearly identical, according to figures provided by the administration.
"Though we cannot verify the claim, (North Korea) wants us to believe that it can launch a thermonuclear strike now, if it is attacked", Adam Mount, a senior fellow at the Center for American Progress, said before the quake.
To back up its bombast, North Korea needs to conduct nuclear tests.
"President Moon also ordered to find ways to nullify North Korea's nuclear facilities and display our military's capability to retaliate".
Rice said that ever since the George W. Bush administration had tried to negotiate denuclearization with the regime's former leader Kim Jong Il, the country has continued its research and development of long-range missiles and bombs. After which, China, Russia, Japan and South Korea strongly condemned NorthKorea's nuclear test.
Moon convened an emergency National Security Council (NSC) meeting, which lasted for one-and-half hours from 1.30 p.m.
In Japan, Shinzo Abe said he "would not tolerate" another nuclear test.
State-run media in North Korea says North Korean leader Kim Jong Un "watched an H-bomb to be loaded into new ICBM". Hours earlier, Pyongyang claimed its leader had inspected a hydrogen bomb meant for a new inter continental ballistic missile. The first of its two atomic tests previous year involved what Pyongyang claimed was a sophisticated hydrogen bomb; the second it said was its most powerful atomic detonation ever.
The key question is how far North Korea has gotten in efforts to consistently shrink down nuclear warheads so they can fit on long-range missiles.