‘High level of activity’ spotted in satellite images at H-bomb facility after Kim Jong Un vowed to retaliate against the West
Iron ore carts, vehicles and construction in the area shows activity is continuing around tunnel entrances that lead to the secretive underground facility
RENEWED activity surrounding North Korea's atomic testing site has sparked fears it is planning a fifth nuclear missile launch.
Satellite images show people and vehicles are working in the area, while visible equipment including iron ore carts suggests tunnel work is underway.
The underground facility, located in the country's southwest, was the site of all four of the country's previous nuclear tests.
Researchers said the images showed a "high level of activity" at the secretive site located deep within the mountainous area.
They were published by , a website run by the US's John Hopkins School of Advanced International Studies.
Researchers wrote it could not be determined what exactly was occurring at the site, and whether it was preparation or maintenance work.
38North reported: "It is clear that North Korea is ensuring that the facility is in a state of readiness that would allow the conduct of future nuclear tests should the order come from Pyongyang."
On January 7 Kim Jong Un staged the country's fourth nuclear test.
He claimed to have launched a potentially devastating "hydrogen bomb" - though this was met with scepticism by experts.
The country was handed down devastating sanctions after the test breached international law.
However, this has only entrenched the standoff between the North and the South and its allies Japan and the US.
Last week diplomatic channels between the US and the North broke down after new sanctions targeting Kim Jong Un personally were established.
We pay for your stories! Do you have a story for The Sun Online news team? Email us at [email protected] or call 0207 782 4368.