A U.S. think tank said on Wednesday that satellite imagery of North Korea's Yongbyon nuclear site provides conclusive evidence that the five-megawatt reactor is in operation. 
  
Beyond Parallel, a project of the Washington-based Center for Strategic and International Studies(CSIS), presented the analysis, citing thermal infrared imagery from September through November.

The report said during the past several months, water discharge from the reactor and probable steam exhaust from the steam turbine and electric generator hall have been observed in visible satellite imagery.

It added that thermal imagery showed that the water is warm water discharge from the reactor's cooling system. 

Beyond Parallel said the imagery also showed continued water discharge into the Kuryong River, and that there were temperature variations of up to four degrees Celsius in the river. 

It said the warmest temperatures in the dispersal pattern are found near the mouth of the water discharge channel outlet and reveal clear indications that the reactor is in operation.