Kyiv's mayor said Russia had fired 60 Iranian-made kamikaze drones at Ukrainian targets, including 36 at the capital, all of which had been shot down. Debris hit apartments and other buildings, injuring at least five people in the capital.
A food warehouse was set ablaze by a missile in the Black Sea city of Odesa, where officials reported three people were injured.
It was the biggest drone swarm yet in a renewed Russian air campaign unleashed 10 days ago after a lull since early March.
Kyiv said Moscow was also making a final push to try to capture the ruined eastern city of Bakhmut, to deliver President Vladimir Putin what would be his only prize for a costly Russian winter offensive, in time for the holiday.
Moscow is preparing for Tuesday's Victory Day parade, the most important day in the calendar for Russia under Putin, who uses the 1945 Soviet triumph over Nazi Germany to justify his invasion of Ukraine.
In a new break with Russia, President Volodymyr Zelenskiy marked Victory Day on Monday rather than Tuesday, announcing that he had signed a decree to change the date of the holiday in line with the practice of Western allies.
"Recalling the heroism of millions of Ukrainians in that war against Nazism, we see the same heroism in the actions of our soldiers today," said Zelenskiy, who addressed the nation from a hilltop overlooking Kyiv.
"Unfortunately, evil has returned. Just as evil rushed into our towns and villages then, so it does now. As it killed our people then, so it does now," he said. "And all the old evil that modern Russia is bringing back will be defeated, just as Nazism was defeated."
The German army's 1945 surrender took effect late at night on May 8 in Berlin, when it was already May 9 in Moscow, the date that became the Soviet holiday.
Russia foreign ministry spokeswoman Maria Zakharova said that by changing the date, Zelenskiy had betrayed the memory of Ukrainians who fought the Nazis.
"What is worse than an enemy? A traitor. That is Zelenskiy, the embodiment of Judas in the 21st century," she said.
Ukraine, as part of the then-Soviet Union, suffered higher per capita casualties than Russia in World War II and was one of the heartlands of European Jewry wiped out in the Holocaust.
On the day of Russia's parade, Zelenskiy will underscore Ukraine's ambition to join the West by receiving European Commission President Ursula von der Leyen, according to the EU which took the unusual step of announcing her war zone visit a day in advance.
Brussels marks May 9 as "Europe Day", honouring a 1950 French declaration that led to the founding of the body that became the EU.
Russia has cancelled or curtailed some of the huge military parades that normally accompany Victory Day.Â
Western countries say this is in part out of security concerns and in part because Moscow has lost so much military hardware in a largely failed winter offensive in Ukraine that has seen the most intense ground combat in Europe since World War II.
"The Russians still hope to capture the city by May 9. Our task is to prevent this," Ukrainian ground forces commander Colonel General Oleksandr Syrskyi said after visiting the front line near Bakhmut, Russia's main target.
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