A U.S.-based North Korean watchdog says recent satellite images indicates "a high-level of activity" at the communist regime's nuclear test site.
A report released Tuesday by 38 North on its website says the images shows what appears to be supplies and/or equipment stacked on the ground at the north section of the Punggye-ri test site, where North Korea conducted nuclear tests in 2013 and 2016.
38 North said "it is not possible to determine whether this activity is for maintenance, excavation or preparation for a fifth nuclear test" based solely on the satellite images. But the group says it is clear that Pyongyang is making sure the Punggye-ri site "is in a state of readiness" for any future tests.
Pyongyang has conducted four known nuclear tests since 2006, the most recent back in January.
Last month, the United Nations' nuclear watchdog, the International Atomic Energy Agency, said satellite evidence shows North Korea has likely resumed activities at a plant at Yongbyon to produce plutonium from spent nuclear reactor fuel.
The information matches evidence found by 38 North, which reported in April that exhaust plumes had been detected from the thermal plant at Yongbyon's main reprocessing installation.