UK & World News
North Korea 'Hides Nuclear Test Site Tunnel'
North Korea has concealed the entrance to an underground nuclear site to prevent satellite monitoring, according to South Korean intelligence sources.
Imagery of the Punggye-ri nuclear test facility in North Hamgyong Province seen by the South Korean officials suggests that covers have been placed over a tunnel entrance.
There is widespread international concern at North Korea's threat to attempt a nuclear detonation - its third since 2006.
Both South Korea and the US are reported to have repositioned intelligence monitoring assets to gain a clear a picture as possible of Pyongyang's intentions.
South Korea's unification minister has said that his government believes the third nuclear test will be much more significant than the first two in 2006 and 2009.
"The first and second tests can be seen as part of Pyongyang's efforts to develop nuclear capability, while a third detonation could mean it is in the final stages," Yu Woo-ik warned.
He said that the third test, which analysts believe might involve the use of uranium rather than plutonium, could fundamentally change the security situation on the Korean peninsula.
North Korea successfully launched a satellite into orbit in December, defying and surprising the international community.
The move prompted the United Nations to levy further sanctions on Pyongyang. The UN resolution had the unusual support of North Korea's only real ally, China.
The Chinese backing is a clear suggestion of Beijing's frustration at North Korea's continued defiance of international law.
The international concern is that North Korea's inexperienced and young new leader Kim Jong-Un plans to combine his two developing technologies - ballistic missile capability and nuclear detonation tests - to create a nuclear weapon.
Pyongyang's rockets already have the ability to reach far across East Asia, though suggestions that they could reach the west coast of the US are thought to be wide of the mark.
Analysts also point out that there is a big technological gap between producing a rocket capable of firing a satellite into orbit and developing a nuclear warhead small enough to fit into a rocket that could then be fired accurately.
In the past, much of what comes out of Pyongyang is seen by Western governments as little more than bluster and rhetoric.
However, the surprise success of December's rocket launch did focus minds in Washington, London, Seoul and even Beijing.
The worry is the significant lack of reliable intelligence emerging from the closed country. Intelligence communities rely on the incomplete picture delivered through the many satellites passing over the peninsula.
Imagery from one satellite does show increased activity at the probable nuclear test site, an analyst told Sky News, but the picture it provides is incomplete.
Information from satellites is useful, but paradoxically, the key questions about how advanced Kim Jong-Un's nuclear programme really is will only be answered once the third test has taken place.