According to Press TV, 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.
South Korea’s Joint Chiefs of Staff said in a statement that the seismic tremor had been detected near the North’s Punggye-ri nuclear test site.
China detected a second tremor, which it said was magnitude 4.6 and came at a depth of zero kilometers eight minutes after the first quake.
While South Korean officials said that the tremors were likely caused by a nuclear explosion, Japan said in certain terms that a nuclear test had occurred.
“After examining the data, we concluded that it was a nuclear test,” Japanese Foreign Minister Taro Kono said at a briefing after a meeting of Japan’s National Security Council.
Japan’s Ministry of Defense said it had dispatched at least three military jets from bases in Japan to test for radiation.
Meanwhile, South Korea’s Yonhap news agency said North Korea was due to make an “important announcement” at 06:30 GMT.
If North Korea confirms that it has conducted a nuclear test, it would be the country’s sixth such test.
Japanese Prime Minister Shinzo Abe had said earlier in the day a nuclear test would be absolutely unacceptable.
“If it forcibly conducted a nuclear test, it’s absolutely unacceptable. We have to strongly protest it,” Abe said.
Just earlier on Sunday, North Korea’s official Korean Central News Agency (KCNA) reported that the country had developed a hydrogen bomb that could be loaded into a new intercontinental ballistic missile.
The developments come amid high tensions over the North Korean missile and nuclear programs.
South Korea, the US, and Japan have been unnerved by the North’s weapons programs, which Pyongyang has been defiantly advancing as countermeasures to their hostility.
On Tuesday, North Korea fired a Hwasong-12 missile — reportedly capable of carrying a nuclear payload — that traveled nearly 2,700 kilometers into the Pacific, including over Japan.
The violation of Japanese airspace sparked angry reactions from Japan and the US, as well as calls for restraint by other countries, including Russia and China. The launch also prompted a United Nations Security Council condemnation.