KYIV, Ukraine (AP) — The head of the U.N. atomic watchdog says conditions at Ukraine’s Zaporizhzhia nuclear power plant are increasingly precarious and a safety zone around it needs to be established immediately to prevent a nuclear accident.

Rafael Mariano Grossi, the director of the International Atomic Energy Agency, said in a statement Friday that there is little likelihood of re-establishing reliable offsite power lines to the plant, and its Ukrainian operator is considering shutting down the only remaining operating reactor.

This would leave the plant fully reliant on emergency diesel generators to provide electricity for vital nuclear safety functions.

“This is an unsustainable situation and is becoming increasingly precarious,” Grossi said.

“The power plant has no offsite power. And we have seen that once infrastructure is repaired, it is damaged once again,” he said. “This is completely unacceptable. It cannot stand.”

Grossi called for an “immediate cessation of all shelling in the entire area” and the establishment of a nuclear safety and security protection zone.

“This is the only way to ensure that we do not face a nuclear accident,” he said.

“Only the withdrawal of the Russians from the plant and the creation of a security zone around it can normalize the situation at the Zaporizhzhia NPP. Only then will the world be able to exhale,” Petro Kotin, the head of Energoatom, said Friday on Ukrainian TV.

Kotin explained in an interview with The Associated Press Thursday that the only operating reactor “can be stopped completely” at any moment and as a consequence of that, the only power source would be a diesel generator.

There are 20 generators on site and enough diesel fuel for 10 days. After that, about 200 tons of diesel fuel would be needed daily for the generators, which he said is “impossible” while the plant is occupied by Russian forces.

Fighting continued Friday in parts of southern and eastern Ukraine and in the north where Ukraine claims to have recently pushed Russian forces out of some areas.

Russian planes bombed the hospital in the town of Velika Pysarivka, on the border with Russia, said Dmytro Zhyvytskyi, governor of the Sumy region. he said the building was destroyed and there were an unknown number of casualties.

In the Donetsk region in the east — one of two that Russia declared to be sovereign states at the outset of the war — eight people were killed in the city of Bakhmut over the past day and the city is without water and electricity for the fourth straight day, said governor Pavlo Kyrylenko.

Four people were killed in shelling in the Kharkiv region, two of them in Kharkiv city, Ukraine’s second-largest, according to regional governor Oleh Syniehubov. The shelling of the city continued on Friday afternoon, its mayor Ihor Terekhov said, wounding 10 people, including three children.

Ukraine this week claimed to have regained control of more than 20 settlements in the Kharkiv region, including the small city of Balakliya.

Social media posts showed weeping and smiling Balakliya residents embracing Ukrainian soldiers.

Kremlin spokesman Dmitry Peskov on Friday refused to comment on the alleged retaking of Balakliya, redirecting all questions about it to the Russian Defense Ministry.

But Vitaly Ganchev, the Russian-installed official in the Kharkiv region, confirmed Friday that “Balakliya, in effect, is not under our control.” Ganchev said that “tough battles” were continuing in the city and that Russian forces were attempting to expel Ukrainian troops.

Ukraine’s National Guard on Friday also confirmed the recapture of Volokhiv Yar, a village 11 miles away from Balakliya.

Ukraine’s presidential adviser Mykhailo Podolyak told Ukrainian television Friday that Ukrainian forces are trying to retake control of Kupianksk — a key city in the Kharkiv region through which Russian troops in the area are receiving all their supplies.

“It is a key transport hub which we need to retake and then see after that whether we should go north or a bit further down south, thus tearing apart this group of Russian troops” and preventing them from replenishing their stock of supplies, Podolyak said.

Helicopters and fighter jets streaked over the rolling plains of the Donetsk region, with the jets heading in the direction of Izium, near where Ukrainian forces have been carrying out a counteroffensive in the Kharkiv region. The jets fired out flares while black smoke billowed in the distance.