Experts and officials have said North Korea could conduct its sixth nuclear test at any time, and that the reclusive country has maintained a readiness at its nuclear test site to conduct another detonation test at any time.
South Korea's presidential office says the security chiefs for Seoul and Washington have spoken following North Korea's sixth nuclear test.
The United States Geological Survey (USGS) on Sunday detected a first tremor, saying in an updated reading that the quake measured 6.3 on the Richter scale at a depth of 10 kilometers, 24 kilometers northeast of Sungjibaegam in North Korea.
North Korea conducted two nuclear tests last year, the last almost a year ago, on the September 9 anniversary of the nation's founding.
North Korean leader Kim Jong Un inspects missiles.
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One expert said the size of Sunday's detonation meant it was possible it could be a hydrogen bomb test.
South Korea's Yonhap News agency says a magnitude 5.6 quake has occurred in North Korea.
The "artificial quake" in North Korea Sunday (Sept 3), which is claimed by North Korea as a successful hydrogen bomb test, was five to six times more powerful than the tremor from Pyongyang's fifth test, the South's weather agency said.
That claim was met with widespread skepticism, but the North has shown significant progress in its nuclear weapons program since then.
"The two leaders reaffirmed the importance of close cooperation between the United States, Japan, and South Korea in the face of the growing threat from North Korea", the White House report on the phone call said.
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Prime Minister Shinzo Abe was quick to express condemnation.
North Korea also tested a nuclear weapon in January of that year.
China's Ministry of Foreign Affairs said in a statement, "The Democratic People's Republic of Korea has once again conducted a nuclear test in spite of widespread opposition from the worldwide community".
"Nuclear Electromagnetic pulse (EMP) has the potential to disrupt, damage, or destroy a wide variety of electrical and electronic equipment", CNN quoted the U.S. Department of Energy statement. Fears of an EMP strike by North Korea have circulated for years among some US policy makers, though others have openly dismissed the possibility of Pyongyang launching such a strike.
Juche is North Korea's homegrown ruling ideology that is a combination of Marxism and extreme nationalism preached by state founder Kim Il Sung, the current leader's grandfather. A day later, President Trump threatened to meet North Korea with "fire and fury".
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