Undeterred by international condemnation of its latest nuclear test and a new round of sanctions, North Korea is reportedly preparing to carry out another underground atomic test.
Satellite images taken since the regime conducted what it claims was a test of a thermonuclear device at its Punggye-ri proving grounds on September 3 have revealed mining equipment and heavy cargo trucks close to a shaft excavated to the south of the test site. Additional activity has also been confirmed at another underground access point, known as the West Portal.
Analysts believe the damage caused by the recent test to subterranean structures beneath Mount Mantap, accessed through the North Portal, is so extensive that it is unsuitable for further tests.
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An analysis of the images by experts from the US-Korea Institute at Johns Hopkins University, released on the 38 North website, confirms "numerous landslides throughout the Punggye-ri Nuclear Test Site on the slopes of Mt. Mantip (and beyond) resulting from North Korea's sixth nuclear test".
The satellite pictures, taken five days after the most recent test, show a "large tractor/trailer cargo truck" at the South Portal, with mining carts and other equipment are visible at the West Portal.
"Such activity, coming shortly after the largest underground conducted at Punggye-ri to date, suggests that onsite work could now be changing focus to further prepare those other portals for future underground nuclear testing", the report states.
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There have also been suggestions in recent days that a Hwasong-14 intercontinental ballistic missiles is being readied at an underground launch facility in Samjiyon, with a South Korean government official confirming to Radio Free Asia that it is "keeping a close watch on North Korean activities and discussing how to react if they provoke again".
Work at the nuclear test site and on another missile launch were under way before the United Nations Security Council imposed new sanctions on North Korea on Monday.
Pyongyang has reacted defiantly to the new restrictions on imports of fuel and lucrative exports of labourers and textile products.
North Korea has said it rejects the UN resolution and state-run media declared it to be a "product of heinous provocation".