North Korea said Sunday that it successfully conducted a test of a hydrogen bomb meant to be loaded onto an intercontinental ballistic missile (ICBM).

The announcement, made on state-run television, came a few hours after a 6.3-magnitude "explosion" was detected in North Korea, according to the United States Geological Survey announced Sunday.

North Korea's leader Kim Jong Un ordered the test, according to the announcement.

South Korea's weather agency, the Korea Meteorological Administration, said on Sunday that the apparent nuclear test appears to have been several times stronger than its previous test.

The agency estimated that the nuclear blast yield of the presumed test was between 50 to 60 kilotons, or five to six times stronger than the North Korea's fifth test, conducted in September 2016.

The seismic activity occurred at 12:29 p.m. local time, just hours after North Korea claimed that 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."

Prior to North Korea's announcement, Japan confirmed that the rogue nation conducted a nuclear test. "It is absolutely unacceptable if North Korea did force another nuclear test, and we must protest strongly," Prime Minister Shinzo Abe said.

And South Korea's Joint Chiefs of Staff had also "presumed" that North Korea did indeed conduct a sixth nuclear test, before its neighbor to the north made the announcement. When news first broke of the seismic activity, South Korea's Joint Chiefs of Staff said the seismic activity was artificial.

The USGS has 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.

Source: AFP