If confirmed, the explosion marks a major step forward in the country’s nuclear development.
“The republic’s first hydrogen bomb test has been successfully performed… based on the strategic determination of the Workers’ Party,” a state television news reader announced.
“With the perfect success of our historic H-bomb, we have joined the rank of advanced nuclear states.
“The latest test, completely based on our technology and our manpower, confirmed that our newly-developed technological resources are accurate and scientifically demonstrated the impact of our miniaturised H-bomb.”
A magnitude-5.1 tremor was earlier detected by the US Geological Survey (USGS) and South Korean officials said they suspected it was an explosion.
“We suspect a man-made earthquake, and are analysing the scale and epicentre of the quake with the geoscience and mineral resource institute of South Korea,” a Korea Meteorological Administration (KMA) official earlier said.
A revised location of the tremor by the USGS puts it at the same location as previous tests in 2006, 2009 and 2013, and at surface depth.
While vowing to stick by a no-first-use policy, North Korea said it would continue to pursue an advanced nuclear strike capability.
“As long as the vicious anti-North policy of the US persists, we will never stop development of our nuclear program,” a statement said.