The announcement from North Korea called the test "an act of self-defense" against foreign threats, according to NPR. Hydrogen bombs — which CNN notes are far stronger than the Atomic bomb dropped on Hiroshima during World War II — are much more powerful than the weapons North Korea has tested in the past."We've joined the rank of nations with nuclear weapons. We won't use the nuclear weapon as long as there's no invasion of our autonomy," the announcement said.

Many experts, however, expressed skepticism about the veracity of the claim, The Associated Press the BBC and other outlets have reported. The quake that followed whatever detonation occurred, several sources said, was far smaller than what a formidable H-bomb would create."The bang they should have gotten would have been 10 times greater than what they're claiming," Bruce Bennett, an analyst with the Rand Corporation, told the BBC . "So Kim Jong-un is either lying, saying they did a hydrogen test when they didn't, they just used a little bit more efficient fission weapon - or the hydrogen part of the test really didn't work very well or the fission part didn't work very well."Still, the announcement was met with widespread condemnation. South Korea pledged to seek additional sanctions from the United Nations Security Council "so that the North will pay the price for the nuclear test," even as its own spy agency expressed doubts about the claim."The test is not only a grave provocation to our national security but also a threat to our future... and a strong challenge to international peace and stability," South Korean President Park Geun-Hye said, the BBC reported.