KYIV - Russian forces attacked Ukraine's energy infrastructure overnight on Saturday, for the second time in less than a week, Ukraine's Energy Minister Denys Shmyhal said.

The strikes targeted the Burshtyn and Dobrotvir thermal power plants in western Ukraine, as well as substations and overhead transmission lines, the minister said.

He further said personnel unloaded units at nuclear power plants as a precautionary measure.

Ukraine's state-run energy company Ukrenergo has requested emergency assistance from Poland in the wake of the attack, Shmyhal added, while the company said it has imposed emergency power outages across most of the country.

The previous attack on Ukraine's energy facilities was carried out on Tuesday.