Drones attacked Zaporizhzhia, Europe's biggest nuclear power plant, on Sunday, hitting a reactor building in the worst such incident since November 2022, though nuclear safety was not compromised, the International Atomic Energy Agency (IAEA) has said.

IAEA Director General Rafael Grossi said that with the end of the winter heating season in nearby Enerhodar, where most plant staff live, unit 4 had been moved from hot shutdown on Saturday, bringing "all six reactor units" to cold shutdown for the first time since late 2022.

"I welcome this development which has been recommended by the Agency for some time, as it enhances the overall safety of the facility," Grossi's statement said.

Cold shutdown allows for an "additional response margin of several days before the cooling of the nuclear fuel in the reactor might be challenged," he added.

The reactor would also need less cooling water than in hot shutdown, he said, an issue that grew more challenging following the destruction of the Kakhovka Dam in June.

However Grossi said the situation at the nuclear plant remained "extremely fragile," noting a team of IAEA experts had heard 16 rounds of outgoing artillery fire in less than half an hour on Saturday, and several drone strikes had targeted the facility over the past week.

The cold shutdown did not address the "fundamental issue of a recent sharp deterioration of the situation at the plant," he said. "Without a doubt, nuclear safety and security at this major nuclear facility remains very precarious."

Moscow and Kyiv have repeatedly accused one another of targeting the plant since Russia seized it weeks after it invaded Ukraine. Both countries requested an emergency meeting of the IAEA's Board soon after Sunday's attack.

(Reporting by Elaine Monaghan in Washington; Editing by Chizu Nomiyama)