KYIV, Ukraine (AP) — The head of the U.N.’s atomic watchdog agency on Sunday condemned a Ukrainian drone strike on one of six nuclear reactors at the Russian-controlled Zaporizhzhia Nuclear Power Plant in Ukraine, saying such attacks “significantly increase the risk of a major nuclear accident."

In a statement on the social media platform X, Rafael Mariano Grossi confirmed at least three direct hits against the ZNPP main reactor containment structures took place. “This cannot happen,” he said.

He said it was the first such attack since November 2022, when he set out five basic principles to avoid a serious nuclear accident with radiological consequences.

Officials at the plant said the site was attacked Sunday by Ukrainian military drones, including a strike on the dome of the plant’s sixth power unit.

According to the plant authorities, there was no critical damage or casualties and radiation levels at the plant were normal after the strikes. Later on Sunday, however, Russian state-owned nuclear agency Rosatom said that three people were wounded in the “unprecedented series of drone attacks,” specifically when a drone hit an area close to the site’s canteen.

The International Atomic Energy Agency said Sunday that its experts had been informed of the drone strike and that “such detonation is consistent with IAEA observations.”

In a separate statement, the IAEA confirmed physical impact of drone attacks at the plant, including at one of its six reactors. One casualty was reported, it said.

"Damage at unit 6 has not compromised nuclear safety, but this is a serious incident with potential to undermine integrity of the reactor’s containment system” it added.

The power plant has been caught in the crossfire since Moscow sent troops into Ukraine in 2022 and seized the facility shortly after. The IAEA has repeatedly expressed alarm about the nuclear power plant, Europe’s largest, amid fears of a potential nuclear catastrophe. Both Ukraine and Russia have regularly accused the other of attacking the plant, which is still close to the front lines.

The plant’s six reactors have been shut down for months, but it still needs power and qualified staff to operate crucial cooling systems and other safety features.

Also on Sunday, three people were killed when their house was hit by a Russian projectile in the front-line town of Huliaipole in Ukraine’s partly occupied southeastern Zaporizhzhia region, regional Gov. Ivan Fedorov said. Later on Sunday, two people were wounded in another shelling of Huliaipole.

Separately, three people were wounded in Russian shelling in Ukraine’s northeast Kharkiv region, according to regional Gov. Oleh Syniehubov.

In Russia, a girl died and four other people were wounded when the debris of a downed Ukrainian drone fell on a car carrying a family of six people in Russia’s Belgorod region bordering Ukraine, regional Gov. Vyacheslav Gladkov said.