The head of the United Nations nuclear watchdog says the Russian-controlled Zaporizhzhia nuclear plant in Ukraine was disconnected to its last external power line.

But the facility is still able to run electricity through a reserve line amid sustained shelling in the area.

International Atomic Energy Agency Director-General Rafael Grossi said in a statement Saturday that the agency’s experts were told by senior Ukrainian staff that the fourth and last operational line was down.

The three others were lost earlier during the conflict.

The I.A.E.A. experts arrived at Zaporizhzhia on Thursday.