A North Korean nuclear test has caused a seismic event in an area in the northeast of the reclusive country. Three previous nuclear tests, in 2006, 2009 and 2013, were conducted in the region.
A televised North Korean statement confirmed the test was a hydrogen bomb test. The test took place at 10 a.m. local time.
The USGS, which measured the event at a magnitude of 5.1, said it occurred 19 kilometers (12 miles) east-northeast of Sungjibaegam.
South Korean foreign ministry hastily convened an emergency meeting, and officials in Japan were also holding discussions.
North Korea’s internationally isolated regime is a heavily militarized state with a huge standing army of 1.2 million active soldiers and 7.7 million reservists.
But its conventional weaponry is dated, with limited effectiveness, and it has looked to developing its nuclear capabilities to project power internationally.
The country declared it had nuclear weapons in 2003, and conducted nuclear tests in 2006, 2009 and 2013.
In May last year, it said it had the ability to miniaturize nuclear weapons, a development that would allow it to deploy nuclear weapons on missiles. A U.S. National Security Council spokesman responded at the time that the United States did not think the North Koreans had such a capability.
David Albright, a former U.N. weapons inspector, told CNN last year that Pyongyang could already have 10 to 15 atomic weapons, and that it could grow that amount by several weapons per year.
He said he believed Pyongyang had the capability to miniaturize a warhead for shorter missiles, but not yet for intercontinental ballistic missiles capable of reaching the United States.