North Korea appears to be continuing operations at its main Yongbyon nuclear complex with signs of some facilities even being expanded, a North Korea information provider said, citing recent satellite imagery. The assessment came amid concerns the recalcitrant and unpredictable regime may carry out another nuclear test in the near future.

Commercial satellite photos taken from April 27 through May 14 of the site, north of Pyongyang, indicate ongoing operations at its 5 MWe reactor as well as expansion efforts, such as the construction of buildings near the experimental light water reactor, according to a recent post by 38 North on its website.

"Taken together, these activities suggest a longer-term investment in further developing the country's nuclear weapons program," it added.

More vehicles have been observed than usual around the 5 MWe reactor and a nearby spent fuel storage building since late April, which include several cargo trucks and as many as three tractor trailers, according to 38 North.

No new activity has been spotted at the experimental light water reactor, which has yet to start operations, but the construction of buildings nearby appears to be ongoing, it said.

"Separate from the reactor, construction continues on a small group of buildings" south of the experimental light water reactor, it said. "The purpose of this small complex is unknown."

South Korea's military has said the North appears to have completed preparations for a new nuclear test. Pyongyang conducted its sixth and last nuclear experiment in September 2017. (Yonhap)