Russia and Ukraine have blamed each other for the attacks over the last week, but it is "impossible" at the moment to prove who is behind them, said International Atomic Energy Agency (IAEA) chief Rafael Grossi.

The largest nuclear power facility in Europe, Zaporizhzhia has been occupied by Russian forces since shortly after their invasion started in February 2022.

It has been shut down since that year amid frequent shelling attacks.

The plant has come under a series of drone attacks since April 7, the first direct assaults on the plant since November 2022.

"These reckless attacks must cease immediately," Grossi told a meeting of the UN Security Council.

"Though, fortunately, they have not led to a radiological incident this time, they significantly increase the risk at Zaporizhzhia nuclear power plant, where nuclear safety is already compromised," said Grossi, whose agency has staff deployed at the facility.

He said the attack "sets a very dangerous precedent" because the reactor confinement structure was hit.

Asked later by reporters about the perpetrators of the attacks, Grossi said "it is simply impossible" to ascertain.

The attacks have been carried out with drones, a device which has "a diverse trajectory. It hovers, it circles."

And drones "can be obtained almost anywhere," said Grossi.

He earlier said that "two years of war are weighing heavily on nuclear safety at Zaporizhzhia nuclear power plant," where "every one of the IAEA's seven pillars of nuclear safety and security have been compromised.

"We cannot sit by and watch as the final weight tips the finely balanced scale," he warned.

"We are getting dangerously close to a nuclear accident. We must not allow complacency to let a role of the dice decide what happens tomorrow," he said.

The risk of a major accident is real even though the reactors are turned off, he said.