The interruption of the power supply, which was restored by midday on Thursday, meant that emergency diesel generators had to be used to cool the plant, had "significantly" increased the risk of a nuclear accident, EU foreign policy chief Josep Borrell said.

"This is a serious breach to the nuclear safety, caused by Russia," Borell told reporters on the sidelines of a meeting the EU's development ministers in Stockholm.

"Zaporizhzhia is the biggest nuclear power plant in Europe... and Russia is putting in danger the entirety of our joint European continent, Russia included," he added.

The strike on the plant came during a fresh wave of Russian attacks across Ukraine which killed at least nine people and led to power outages across the country.