The country has been under UN Security Council sanctions since its first atomic device test in 2006.
A seismic tremor was recorded in an area around North Korea's known nuclear site on Friday, and was suspected to be the fifth nuclear test by the isolated nation, South Korea's Yonhap news agency said. US, European and Chinese seismological agencies reported that the tremor was recorded at 0030 GMT at surface level.
AP reports that North Korea says it has conducted a "nuclear warhead explosion" test meant to counter what Pyongyang calls US hostility.
A South Korean government official said it was a suspected nuclear test, Yonhap reported, and Seoul called for an emergency National Security Council meeting. The China Earthquake Networks Center said the tremor was a suspected explosion. Japan's top government spokesman also said there was a high possibility the seismic event indicated that North Korea had conducted a nuclear test and that relevant ministries had been instructed to gather information.
Two months ago, US-based 38 North, a North Korea monitoring project, said satellite images showed a high level of activity at North Korea's nuclear test site, called Punggye-ri. Speculation has intensified that North Korea may conduct a fifth nuclear test after the United States blacklisted its leader, Kim Jong Un, on July 6 for human rights abuses.
North Korea conducted its fourth nuclear test in January, resulting in tough new UN sanctions. It has conducted a series of missile tests this year, including a submarine-launched missile. The January test was recorded with a magnitude of 5.1, according to the US Geological Survey.
North Korea has been under UN Security Council sanctions since it first tested an atomic device in 2006.
United States
The White House's National Security Council said on Thursday it was aware of seismic activity on the Korean Peninsula in the vicinity of a known North Korean nuclear test site.
"We are monitoring and continuing to assess the situation in close coordination with our regional partners," an NSC statement said.NSC statement said.
South Korea
South Korea's military believes North Korea has conducted its fifth nuclear test, and the 5.0 magnitude seismic event on Friday indicated the blast was 10 kilotonnes in yield, the largest ever conducted by the North, Yonhap news agency said. South Korea's military could not immediately confirm the report.
South Korea will make diplomatic efforts for stronger UN Security Council sanctions on North Korea, Yonhap news agency reported citing the South's foreign ministry
China
China's environment ministry has begun emergency radiation monitoring along border regions in northeastern China after North Korea carried out a suspected nuclear test, state television said on its official microblog on Friday.
Japan
Prime Minister Shinzo Abe said on Friday that a suspected nuclear test by North Korea could not be tolerated and that Japan would protest strongly to Pyongyang if confirmed. A seismic tremor was recorded in an area around North Korea's known nuclear site on Friday, and was suspected to be the fifth nuclear test by the isolated nation.
Japanese Foreign Minister Fumio Kishida said on Friday that Tokyo has protested to North Korea over the secretive country's suspected latest nuclear test. Such a test, if confirmed, would breach UN resolutions and pose a grave challenge to global nuclear non-proliferation efforts, Kishida told reporters.
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