A U.S.-based North Korea monitoring website says a number of unusual activities appear to have occurred over the past several years around a previously abandoned reactor at the Yongbyon Nuclear Scientific Research Center.

38 North presented the assessment on Friday citing commercial satellite imagery. 

The site said that an eight by six meter hole appeared in the roof of the reactor building sometime between February and June 2018 and a second circular structure that appears to be a water holding tank was erected next to a small administrative or support building in December that year.

New trenching was reportedly noted around October 2019 near the reactor building and an adjacent building built in 2015 that was likely used for administration was razed in late October or early November 2019.

38 North said that activity at the Yongbyon site is not out of the ordinary, noting a 2005 effort by North Korea to create the false impression that it was working to restart construction of the reactor.

The site said that while the purpose of the latest activities are unknown, they are unlikely related to renewed construction.