The Zaporizhzhia Nuclear Power Station in southeastern Ukraine. AFP
In a phone call, the four leaders also called for a "quick visit" to the nuclear site by independent inspectors of the International Atomic Energy Agency, said German Chancellor Olaf Scholz's spokesman.
A flare-up in fighting around the Russian-controlled nuclear power station, with both sides blaming each other for attacks, has raised the spectre of a disaster worse than in Chernobyl.
On Friday, the French presidency said Russian President Vladimir Putin has agreed that IAEA inspectors can travel to the nuclear plant for an inspection.
During their talks on Sunday, Scholz, US President Joe Biden, French President Emmanuel Macron and British Prime Minister Boris Johnson also "agreed that support for Ukraine in its defence against Russian aggression would be sustained".