North Korea appears to be continuing the operation of a plutonium-producing nuclear reactor at its mainstay Yongbyon complex, a US monitoring website has said, citing satellite imagery.

38 North reported Wednesday recent commercial satellite imagery of the complex north of Pyongyang provided further evidence of activity at the 5-megawatt reactor, which can produce up to 6 kilograms of plutonium -- a fissile material used for a bomb -- a year.

"Steam is emanating from the reactor's generator hall, indicating that at least one of the generators is running," the website said. "Additionally, water continues to be discharged from the auxiliary pipe into the channel leading to the Kuryong River."

The website said the new activity at the rector is "notable," as production of fissile materials is likely needed to accomplish North Korean leader Kim Jong-un's goal of strengthening nuclear capabilities announced during the country's eighth party congress in January.

Construction of a new wing south of the experimental light water reactor seems to continue, although there are no signs of operations starting at the facility, it noted.

The suspicion is in line with the monitoring results by the International Atomic Energy Agency (IAEA), which said the North appears to have continued operations at the Yongbyon nuclear reactor since it went into operation in August.

The UN nuclear watchdog also pointed out nuclear activities at the nation's uranium enrichment and mine facility elsewhere.

"There are ongoing indications of activities at the Kangson complex and the Pyongsan Mine and Concentration Plant," IAEA Director-General Rafael Grossi said during a board of governors meeting Wednesday.

The Kangson complex is North Korea's second uranium-enrichment plant after its well-known facility in Yongbyon, and the Pyongsan facility is a major mill that turns uranium ore into yellowcake, a first step toward enriching uranium. (Yonhap)