A strike that killed six was the latest in a series of aerial assaults, many of which have targeted the power grid in an effort to deprive Ukrainians of energy as winter looms.

Russia unleashed a major missile and drone barrage on Kyiv early Friday, killing four people, starting fires and scattering debris as the sound of explosions boomed across the city, Ukrainian authorities said.

Russia's Black Sea port of Novorossiysk temporarily suspended oil exports - equivalent to 2.2 million barrels per day, or 2% of global supply - on Friday, according to industry sources, after a Ukrainian missile and drone attack.