Ukraine’s Zaporizhzhia Nuclear Power Plant, Europe’s largest atomic power station, spent hours operating on emergency diesel generators Monday after losing its external power supply for the seventh time since Russia’s full-scale invasion of its neighbor, the head of the U.N. nuclear watchdog said.

“The nuclear safety situation at the plant (is) extremely vulnerable,” Rafael Grossi, head of the International Atomic Energy Agency, said in a tweet.

Hours later, national energy company Ukrenergo said on Telegram that it had restored the power line that feeds the plant.

But for Grossi, it was another reminder of what’s at stake at the Russian-occupied plant which has seen shelling close by.

“We must agree to protect (the) plant now; this situation cannot continue,” Grossi said, in his latest appeal for the area to be spared from the fighting between Ukrainian and Russian forces. IAEA staff are deployed at the plant, which is occupied by Russian troops.

The plant’s six nuclear reactors are protected by a reinforced shelter able to withstand an errant shell or rocket. But a disruption in the electrical supply could disable cooling systems essential for the reactors’ safety. Emergency diesel generators, which officials say can keep the plant operational for 10 days, can be unreliable.

Fighting, especially artillery fire, around the plant has fueled fears of a disaster like the one at Chernobyl in 1986. Then, a reactor exploded and spewed deadly radiation, contaminating a vast area in the world’s worst nuclear catastrophe.

Energoatom, Ukraine’s state nuclear company, blamed Russian shelling for the loss of the last high-voltage transmission line to the plant in Russian-occupied southern Ukraine, about 500 kilometers (300 miles) from Kyiv. It was not possible to independently verify that claim.

The facility is “on the verge of a nuclear and radiation accident,” Energoatom warned.

Grossi said it was the seventh time the plant had lost its outside power supply since Russia’s full-scale invasion in February 2022.

The Zaporizhzhia Nuclear Power Plant is one of the 10 biggest atomic power stations in the world.

Russian officials have begun training for a planned evacuation from the plant of 3,100 staff and their families, a representative of Energoatom said last week. The plant employed around 11,000 staff before the war, some 6,000 of whom remain at the site and in the surrounding town of Enerhodar.

More Russian military units have been arriving at the site and are mining it, the representative told The Associated Press, speaking on condition of anonymity due to security concerns.

Ukraine’s presidential office said Monday morning that at least three Ukrainian civilians were killed and 16 others were injured over the previous 24 hours.

The Ukrainian Air Force reported that four out of 16 Russian missiles and all 20 drones launched against Ukrainian targets were shot down.

Military targets and public infrastructure in Dnipro, Ukraine’s fourth-largest city in the center of the country, were singled out for Russian attacks, which injured eight people, officials said. The Dnipro fire department was affected, and 12 houses, shops, and a kindergarten were damaged, according to Governor Serhii Lysak.

(AP)