Ukrainian officials said Russia launched more than 200 drones overnight on Tuesday, putting an end to hopes that the three-day ceasefire that ended on Monday would be extended.
Ukrainian President Volodymyr Zelenskiy, meanwhile, said his country's forces had struck gas facilities in Russia's central Orenburg region, more than 1500km from its borders.
A drone attack on an apartment building in Zelenskiy's hometown, the central Ukrainian city of Kryvyi Rih, killed two and injured four, including the dead couple's nine-month-old granddaughter, regional governor Oleksandr Hanzha and the head of the military administration, Oleksandr Vilkul, said on Telegram.
The child's leg was severed.
Zelenskiy, also writing on X, denounced the strike as "cynical and devoid of all military logic".
"After the end of the partial three-day ceasefire, Russia continues to kill and maim Ukrainians and pressure on it must therefore in no way be weakened," he said.
Northeast of Kryvyi Rih, an aerial bomb strike killed four and injured three, Hanzha said.
Ukraine and Russia had agreed to the ceasefire linked to the anniversary of the Soviet victory over Nazi Germany in World War Two, part of a US-led push for peace under President Donald Trump after more than four years of war.
Trump said on Friday he hoped the truce would be extended.
Although neither side reported large-scale airstrikes during the ceasefire, both said fighting continued along the front line, accusing each other of drone and artillery attacks.
Zelenskiy, speaking in his nightly video address, said Kyiv was working with its allies in Europe to develop technologies to defend against ballistic missiles, adding that 13 countries and NATO representatives had participated in talks on the issue on Tuesday.
Ukrainian Foreign Minister Andrii Sybiha said Kyiv had proposed extending the truce, but Moscow instead escalated by targeting civilian infrastructure with more than 200 drones.
Zelenskiy said drones were intercepted over several regions but reported damage to energy facilities, apartment buildings, a kindergarten and a civilian locomotive.
In Kyiv, debris from a downed drone fell on the roof of a 16-storey residential building in the northern Obolon district, sparking a fire, Mayor Vitali Klitschko said.
Two people were hurt in the central Cherkasy region and damage was also recorded in Zhytomyr region, further west, and in Chernihiv region on the Russian border.
Two people were injured in strikes on the southeastern city of Dnipro and the southern city of Kherson. Russian drones also hit energy infrastructure in the Mykolaiv region, causing blackouts in the region, regional governor Vitaliy Kim said.
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