Images showed vehicles not often seen except during preparations for a test.
A fifth North Korea nuclear test could be around the corner, according to an analysis of satellite imagery.
On 38 North, a Johns Hopkins University website dedicated to North Korea issues, analyst Joseph S. Bermudez wrote commercial imagery from May 5 showed new levels of activity at Punggye-ri nuclear site.
There are vehicles at what is thought to be the Command Center, Bermudez wrote.
“While the historical record is incomplete, it appears that vehicles are not often seen there except during preparations for a test,” the analyst said.
Similar vehicles were seen near the North Portal of the test site during Pyongyang’s second, third and fourth nuclear tests, Yonhap reported.
On May 5, the images showed low levels of activity about 20 meters from the North Portal.
“The crates or trailers seen in this area in previous imagery are no longer present,” Bermudez wrote.
In a previous analysis, Bermudez and analyst Jack Liu stated that the low levels of movement at the site could either mean all preparations for a test are complete or that Pyongyang is engaging in “normal maintenance work.”
Analysts in the United States and South Korea have said it’s likely a test could be conducted in May.
On Friday, at North Korea’s Seventh Party Congress, leader Kim Jong Un said in a speech “unprecedented results have been accomplished” and with “great success” in nuclear tests.