WASHINGTON -- North Korea's decommissioned nuclear test site in Punggye-ri shows signs of routine security patrols, a US monitor said Wednesday.

In commercial satellite imagery from Jan. 17, footpaths and vehicle tracks were visible in the snow around the portal areas and at the main administrative support area, 38 North said on its website.

The imagery also showed snow-cleared roads leading from the security barracks area to the command center, it said.

"There are no indications of renewed excavation, construction or other activity that would suggest the North is trying to reopen the complex," 38 North added. "Instead, track activity is more likely related to security patrols of the area."

The monitor especially pointed to footpaths in the snow leading up to the East Portal, saying it is very rare to see evidence of activity there due to roads being blocked by landslides and displaced boulders for several years.

The East Portal, it said, is the tunnel that was used to conduct North Korea's first nuclear test in 2006.

"While it is unclear why personnel would be in this area, one possibility is that it may be part of routine security patrols," 38 North said.

North Korea demolished the site in front of a group of foreign journalists in May 2018 to demonstrate its commitment to denuclearization.

Earlier Wednesday, a minor natural earthquake of magnitude 2.5 was detected some 3 kilometers southeast of the facility, according to South Korea's meteorological office. The tremor was presumed to be the result of altered seismicity following the North's sixth and latest nuclear test in September 2017. (Yonhap)