The head of the UN’s atomic watchdog agency has said a drone attack on one of six nuclear reactors at the Russian-controlled Zaporizhzhia Nuclear Power Plant in Ukraine “significantly increases” 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 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.

In a separate statement, the International Atomic Energy Agency (IAEA) confirmed the 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 the integrity of the reactor’s containment system” it added.