North Korea : conducts successful test of hydrogen bomb
North Korea said on Wednesday it had successfully carried out its first hydrogen bomb test, marking a major step forward in its nuclear development, if confirmed.
"The republic's first hydrogen bomb test has been successfully performed at 10:00 am on January 6, 2016, based on the strategic determination of the Workers' Party," a state television news reader announced.
The announcement comes hours after a 5.1 magnitude tremor was detected close to North Korea's nuclear test site.
The US Geological Survey said the epicentre of the quake - detected at 10:00am Pyongyang time (0130 GMT) - was in the northeast of the country, some 50 kilometres (30 miles) northwest of Kilju city, placing it right next to the Punggye-ri nuclear test site.
The website of the China Earthquake Network Centre described it as a "suspected explosion".
The North has conducted three nuclear tests in 2006, 2009 and 2013 - all at the Punggye-ri site.
Researchers at the US-Korea Institute at Johns Hopkins University said last month that recent satellite images showed North Korea was excavating a new tunnel at Punggye-ri.
"While there are no indications that a nuclear test in imminent, the new tunnel adds to North Korea's ability to conduct additional detonations over the coming years if it chooses to do so," they said at the time.
North Korea had conducted its third nuclear test in February 2013.
The 'hydrogen bomb test' is likely to further North Korea's international isolation by prompting a push for new, tougher sanctions at the United Nations and worsening Pyongyang's already bad ties with Washington and its neighbors.
Pyongyang is thought to have a handful of crude nuclear weapons. The United States and its allies worry about North Korean nuclear tests because each new blast brings the country closer to perfecting its nuclear arsenal.
Since the elevation of young leader Kim Jong Un in 2011, North Korea has ramped up angry rhetoric against the leaders of allies Washington and Seoul and the U.S.-South Korean annual military drills it considers invasion preparation.