Signs of a large amount of digging at North Korea's nuclear test site can be seen in new satellite images, though the purpose is not yet clear.
A "significant acceleration in excavation activity" can be seen at the "West Portal" area of the Punggye-ri testing grounds, wrote image expert Jack Liu in a Thursday analysis posted on the specialist website 38 North, which monitors developments at North Korea's nuclear weapons-related sites.
Compared to images of the nuclear test site taken in December, "the size of the pile of spoil excavated from a new tunnel appears to have doubled in a period of a little over a month," Liu wrote. "Spoil" refers to excavation debris.
"When last viewed in early December 2013 there were no signs of test preparations," said the report by "38 North," a website project of the U.S.-Korea Institute at Johns Hopkins University.
Still, it is doubtful, according to Liu, that North Korea would use the emerging tunnel for a fourth underground atomic explosion, when it already has two other finished tunnels ready for use in the southern part of the testing grounds.
There could be a number of reasons for the faster digging speed, the image analyst said, such as a need to meet a deadline for completing the tunnel or because the rock and dirt became easier to shift.
South Korean Defense Minister Kim Kwan-jin earlier this week said Pyongyang did not appear to be planning a nuclear test in the imminent future, though it was technically ready to carry one out.
Were North Korea to make the political decision to conduct a test, certain preparations would likely be taken at Punggye-ri in the weeks and days beforehand, such as the placement of camouflage netting over the tunnel entrance and the erection of a satellite dish nearby in order to transmit technical data from the blast site, Liu said.
There also probably would be a general uptick in the personnel activity and vehicle traffic at the test site. No such indicators of an imminent nuclear explosion can be seen in the most recent photographs, he said.
While international scientists view the North's first two atomic tests to have been partial failures at best, the third nuclear blast last February was seen to be more successful, due to its substantially greater yield. Defense specialists say that with every test it conducts, Pyongyang is advancing toward the ability to build nuclear warheads small enough for mounting on missiles.
This article was published in Global Security Newswire, which is produced independently by National Journal Group under contract with the Nuclear Threat Initiative. NTI is a nonprofit, nonpartisan group working to reduce global threats from nuclear, biological, and chemical weapons.