January 2016 North Korean nuclear test

[9] North Korea had previously conducted three underground nuclear tests in 2006, 2009, and 2013, drawing sanctions from the United Nations Security Council.

[16] In a New Year's Day speech, Kim Jong Un warned that provocation from "invasive outsiders" would be met with a "holy war of justice".

[22][23] Won-Young Kim at the Lamont–Doherty Earth Observatory explained it "was more powerful than North Korea's previous nuclear test" and added that it is difficult to quantify "the exact size of North Korea's nuclear detonations because the depth of the explosive device, properties of the rock surrounding the explosion and other factors influence the seismic measurements produced" because North Korea does not publicize the depth of its tests, although the material at the Punggye-ri Nuclear Test Site is thought to be hard granite.

[25] China Central Television released photos of students being evacuated in the area and stated that the ground at a local high school showed cracks.

[13][26] Andre Gsponer of the Independent Scientific Research Institute at the University of Oxford said this technology has "a number of significant technical and military advantages, which explain why it is used in essentially all militarized nuclear weapons, including in India, Pakistan, and North Korea".

"What we're speculating is they tried to do a boosted nuclear device, which is an atomic bomb that has a little bit of hydrogen, an isotope in it called tritium," said Joseph Cirincione, president of the global security firm Ploughshares Fund.

Admiral Bill Gortney, head of US Northern Command and the North American Aerospace Defense Command, said in October 2015 he believed North Korea had rockets with enough range to hit the continental US and added that "the secretive state had already developed 'miniaturised' nuclear bombs that could be fitted to these rockets".

[34] Jeffrey Lewis, expert at the Center for Nonproliferation Studies, said that a boosted fission weapon is "the most likely scenario in my view, with a failed thermonuclear test a close second".