A 6.3-magnitude "explosion" has been detected in North Korea, the United States Geological Survey announced Sunday.
The seismic activity occurred at 12:29 p.m. local time, just hours after North Korea claimed that leader Kim Jong Un had inspected the loading of a hydrogen bomb into a new intercontinental ballistic missile.
According to the USGS, the seismic activity — which the scientific agency has not identified as an earthquake per se — occurred 24 kilometers east northeast of Sungjibaegam, North Korea.
"Possible explosion, located near the site where North Korea has detonated nuclear explosions in the past," read a statement on the USGS website. "If this event was an explosion, the USGS National Earthquake Information Center cannot determine its type, whether nuclear or any other possible type."
Japan confirmed that North Korea conducted a nuclear test, Foreign Minister Taro Kano said, according to The Associated Press. "It is absolutely unacceptable if North Korea did force another nuclear test, and we must protest strongly," Prime Minister Shinzo Abe said.
And according to South Korea's Yonhap news agency, the country's Joint Chiefs of Staff say North Korea is "presumed" to have conducted a sixth nuclear test. When news first broke of the seismic activity, the Joint Chiefs of Staff said the seismic activity was artificial.
The USGS told ABC News Radio they it detected a second event about eight minutes after the 6.3-magnitude "explosion," but it was too small to narrow down a location and magnitude.
South Korea's presidential office said it will hold a National Security Council meeting chaired by President Moon Jae-in.
The North Korean government released photos earlier Sunday of Kim Jong Un talking with his lieutenants as he watched a silver, peanut-shaped device that was apparently the purported thermonuclear weapon destined for an ICBM. What appeared to be the nose cone of a missile could also be seen near the alleged bomb in one picture. The photo could not be independently verified. Another photo showed a diagram on the wall of a bomb mounted inside a cone.
North Korea conducted its fifth test in September 2016. That test was one of two tests conducted last year.
ABC News' Michael O'Keefe contributed to this report.
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