A new satellite image appears to show signs of further activity at North Korea's Punggye-ri Nuclear Test Facility.
According to the Center for Strategic and International Studies, the image acquired on Tuesday shows new construction work at Tunnel Four.
It also said renovations in Tunnel Three, which began around four months ago, appear to be complete.
South Korea and others have already concluded that the regime is ready to conduct its first nuclear test since 2017.
The four tunnels at the site, used for nuclear testing, are believed to have been at least partially collapsed when North Korea claimed to have disabled the site in 2018.