Russian forces have damaged a high-voltage line connecting Ukraine’s Chernobyl nuclear power plant to the power grid, Ukraine’s state energy company Ukrenergo said.

The head of Ukrenergo, Volodymyr Kudrytskiy, said the plant was relying on electricity from diesel generators after external power supplies to the plant were damaged again. The retired nuclear plant lost power early last week but supply was restored on Sunday, the International Atomic Energy Agency confirmed.

It said Ukrainian specialist teams had succeeded in repairing a power line needed to resume external electricity supplies to Chernobyl, four days after they were completely lost at the Russian-controlled site.

But in a statement posted on Facebook, the energy operator said: “The line that supplies the Chernobyl nuclear power plant and the town of Slavutych was damaged by the occupying forces.”