According to the U.N. nuclear inspector, continuous shelling has caused Ukraine’s largest nuclear power plant, Zaporizhzhia, to lose its final external power source. It now depends solely on emergency diesel generators.

The plant’s connection to a 750-kilovolt line was severed around one in the morning on Saturday. In addition to findings from IAEA experts present at the site, which is controlled by Russian forces, it cited official information from Ukraine, the International Atomic Energy Agency claims.

Although the plant’s six reactors are all off, power is still needed for cooling and other safety-related operations. Plant engineers are repairing the damaged power line and the plant’s generators; even if not all of them are now in service, each has enough fuel for at least ten days, according to the IAEA.

IAEA Director-General Rafael Grossi said in a statement that “the resumption of bombardment, attacking the plant’s sole source of external electricity, is extremely irresponsible.”

Grossi paid for a trip to Kyiv on Thursday. To advance his campaign to create a “nuclear safety and security protection zone” surrounding the plant, which he has advocated for weeks, he claimed he would shortly fly to Russia and then make another journey to Ukraine. “This is an absolute and urgent imperative,” he said.

The IAEA didn’t assign the bombardment blame.

One of the four areas Russian President Vladimir Putin annexed in defiance of international law is Zaporizhzhia. The same-named city is still under Ukrainian authority even though the nuclear plant has been under Russian control for months.

Putin declared that Russia would take control of the plant in an order he signed on Wednesday. It was described as a criminal act by the Ukrainian Foreign Ministry, which also declared Putin’s mandate to be “null and void.” Energoatom, Ukraine’s government-run nuclear power company, announced that it would keep running the reactor.