The Ukrainian capital Kyiv came under ballistic missile attack from Russian forces early on Sunday, while other regions suffered bombardments later during the day that killed two people.
Russia, for its part, said four people were killed by a Ukrainian drone strike in the Russian-occupied Ukrainian city of Horlivka.
Ukraine's air force said Russian forces had targeted the capital with ballistic missiles, as explosions rocked the city.
In its morning note, the air force said Russia had launched seven ballistic missiles and 136 drones at Ukraine overnight.
In the eastern city of Kharkiv, one person was killed and 12 others required medical attention after a daytime drone attack.
Meanwhile, a glide bomb attack killed one person and wounded six in the southern city of Zaporizhzhia, which has been under heavy bombardment in recent months.
Kyiv Mayor Vitali Klitschko said one blaze had broken out on the seventh and eighth floors of a multi-storey apartment block in a central district after the overnight missile attack.
Three people were wounded in the capital, and unofficial social media channels showed footage of fires burning.
President Volodymyr Zelenskiy had warned on Friday that Russian attacks were likely over the next 48 hours.
In Horlivka, a city in the Russian-occupied part of Ukraine's Donetsk province, Russian-installed Mayor Ivan Prikhodko said four civilians had been killed in a Ukrainian drone strike, Russia's TASS news agency reported. Prikhodko gave no further details.
On Saturday, Russian-installed authorities accused Ukraine of deliberately attacking civilians after 12 people were killed in a drone attack on a holiday camp in a Russian-held part of Ukraine's Zaporizhzhia region.
Both Russia and Ukraine deny targeting civilians in the war launched by Russia's full-scale invasion in February 2022.
Thousands of civilians have died, most of them Ukrainians killed in Russian attacks.
