UN nuclear agency chief Rafael Grossi said after visiting Russia’s Kursk nuclear power plant on Tuesday that there was a risk of a nuclear accident and the situation was serious.

“The danger or possibility of a nuclear accident has emerged near here,” Grossi told reporters, referring to the fact that fighting is taking place in the surrounding Kursk region.

Russia says the plant has been repeatedly attacked by Ukrainian forces that are just 40 km away after carving out a slice of Russian territory this month. Ukraine has yet to respond to the accusations.

Grossi, head of the International Atomic Energy Agency, told a news conference that the plant was extremely fragile because it had no protective dome.

He said the site was currently still operating very close to normal conditions, but this meant that the situation regarding its security was even more serious.

Russian state nuclear company Rosenergoatom said Grossi had been able to satisfy himself that the plant’s Number Three reactor was working at planned capacity, while its fourth reactor has been undergoing scheduled maintenance since Sunday. He was also shown a new reactor block that is under construction, it said.

The chief of Ukraine’s army said on Tuesday that the country’s troops control nearly 1,300 sq km of Russia’s Kursk region since their surprised incursion three weeks ago.

Gen. Oleksandr Syrskyi also said that Ukraine has captured 594 Russian prisoners in its operation.

“The enemy drags troops from other directions, in such way weakening them. They attempt to create a ring of defence around our offensive group of troops and plan counteroffensive actions,” Syrskyi said, commenting on the situation in the Kursk region.

The seized territory is roughly the size of Los Angeles.

His claim, which could not be independently confirmed, came hours after Ukraine endured a second consecutive barrage of nighttime air and missile attacks from Russia.