Seoul: North Korea today said that it had successfully carried out its first hydrogen bomb test, marking a major step forward in its nuclear development.
A state-run TV news reader announced that the republic's first hydrogen bomb test has been successfully performed at 10:00 am on January 6, 2016.
North Korean government officials, however, refused to confirm whether a nuclear blast or natural earthquake had taken place. But they said that an 'important announcement' will be made later in the day.
The South Korean government officials said that they detected an 'artificial earthquake' near North Korea's main nuclear test site, a strong indication that nuclear-armed Pyongyang had conducted its fourth atomic test.
An official from the Korea Metrological Administration, South Korea's weather agency, said it believed the earthquake was caused artificially based on their analysis of the seismic waves and that it originated 49 kilometers (30 miles) north of Kilju, the northeastern area where North Korea's main nuclear test site is located.
A confirmed test would mark another big step toward Pyongyang's goal of building a warhead that can be mounted on a missile capable of reaching the US mainland.
The Japanese government too said that an earthquake recorded in North Korea might have been caused by a nuclear test.
"Considering past cases, there is the possibility that this might be a nuclear test by North Korea," Chief Cabinet Secretary Yoshihide Suga, the government's top spokesman, said at a regular briefing, adding that Tokyo was analysing the situation.
The US Geological Survey measured the magnitude of the seismic activity at 5.1 on its website.
North Korea conducted all three previous atomic detonations there. The third nuclear test was conducted in February 2013.
Another test would 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.
With Agency Inputs