A key energy facility and a residential building in the outskirts of Kyiv have been hit by overnight Russian missile and drone strikes.
In the capital, at least three people were killed and 21 injured, Ukraine's state emergencies service DSNS said. At least 600,000 people across the country are without electricity after strikes hit critical infrastructure in the Kyiv region and the north-eastern city of Kharkiv.
The strikes come after US President Donald Trump said on Sunday that an "energy ceasefire" was in place between Russia and Ukraine.
Russia's defence ministry said its "massive" strikes had targeted communications and energy facilities used by Ukraine's military.
BBC Ukraine Correspondent Dan Johnson explains.
Read more on this story: Russian strikes leave 600,000 without power in Ukraine, Zelensky says