Russian missiles knocked out the power supply to Europe's largest nuclear plant during a barrage of strikes targeting cities across Ukraine on Thursday, while Ukrainian defenders repelled fierce assaults on the beleaguered town of Bakhmut.

The Zaporizhzhia nuclear power plant, which Russian forces captured a year ago, was left depending on back-up generators after Russian missiles damaged Ukrainian infrastructure that had been delivering electricity to the plant, Ukrainian state power company Energoatom said in a statement.

"The last link between the occupied Zaporizhzhia Nuclear Power Plant (ZNPP) and the Ukrainian power system was cut off," Energoatom said in a statement.