North Korea appears to be continuing the operation of a plutonium-producing nuclear reactor at its Yongbyon complex, according to a U.S. monitoring website.

Citing satellite imagery from Wednesday, 38 North reported that there's further evidence of activity at the 5-megawatt reactor.

"Steam is emanating from the reactor's generator hall, indicating that at least one of the generators is running," it said.

It can produce up to 6 kilograms of plutonium, a fissile material used for a bomb, a year.

38 North said the new activity is "notable" as production of fissile materials is likely needed to accomplish leader Kim Jong-un's goal of strengthening his country's nuclear capabilities.