Russia has denied any responsibility for the attack. The head of the UN-backed international atomic energy watchdog, IAEA – which has a team based at the former Soviet nuclear site in Ukraine – issued a statement confirming that the strike had caused a fire, describing it as “a deeply concerning incident that underlines the persistent risks to nuclear safety during the military conflict.”

IAEA Director General Rafael Mariano Grossi said the team heard the explosion at 1:50am local time followed by smoke and associated fire visible from their dormitory rooms.

“Fire safety personnel and vehicles arrived at the scene within minutes to extinguish the blaze, which still could be seen intermittently for several hours afterwards,” Mr. Grossi added.

Radiation levels ‘normal and stable’

Radiation levels inside and outside the so-called New Safe Confinement building “remain normal and stable,” the team was told, and there are no reports of any casualties or radiation leak.

The damaged cladding around reactor unit 4 was built to seal in the radioactive material from the 1986 fire and meltdown and is intended to last for many generations.

Russian forces briefly occupied the area around Chernobyl shortly after invading Ukraine, but it was recaptured in March 2022.

The Chernobyl plant suffered one of the world’s worst nuclear accidents which saw radiation leak into the atmosphere, contaminating an 18-mile zone which local residents and workers were forced to leave.

The explosion sent radioactive material high into the atmosphere and triggered a public health emergency across the whole of Europe.

Referring to Friday's strike, the IAEA team on site "could see a breach of the outer layer of the NSC that occurred following the detonation,” Mr. Grossi continued. “Supplementary information from Ukraine’s regulatory body received this morning confirmed that the outer cladding of the NSC arch sustained damage, and investigations are ongoing to determine the status of the inner cladding.”

Constant threat

Coming soon after a recent increase in military activity near Ukraine’s Zaporizhzhya Nuclear Power Plant (ZNPP), Director General Grossi said it once again demonstrated that nuclear safety remains under constant threat for as long as the conflict continues.

“There is no room for complacency, and the IAEA remains on high alert,” he said. “I once again call for maximum military restraint around Ukraine’s nuclear sites.”

The agency said it would continue to provide updates as new information becomes available.