Ukraine’s state operator Energoatom said on Thursday that a Russian mine exploded near the generator room of the vast Russian-controlled Zaporizhzhia nuclear plant.

“According to sources, an explosion happened near the engine room of the fourth (reactor) power unit,” Energoatom said in a statement.

It also said Russian troops, who last year seized control of Ukraine’s largest nuclear complex, told workers that it was “their own mine that detonated.”