Iran had to unload fuel from the reactor at the Bushehr power plant in late February, the latest delay to hit the project. The giant plant was meant to start feeding electricity into the national grid in the same month.
The fuel was provided by Russia, which built the plant.
Russia said a breakdown in one the reactor's cooling pumps necessitated the removal of 163 fuel rods from its core, according to the report.
Envoy Alexander Sadovnikov said it was better to solve the problem now in order to prevent similar setbacks happening in the future.
"We will finish the project in the near future," Sadovnikov said
"It is as much an objective for us as it is for Iran," he added.