At least 12 people were killed and more than a dozen others, including children, were wounded when Russia launched overnight missile and drone strikes across Ukraine from Friday into Saturday.
Ukrainian President Volodymyr Zelenskyy said Russia had launched 29 missiles and 480 drones, several of which targeted energy and railway infrastructure.
Authorities in Kharkiv, the second-largest city, said a ballistic missile strike destroyed a five-storey apartment block, killing 10 people.
AFP reporters saw rescuers sifting through the debris, where several people were believed to be trapped.
"Since last night, the rubble of a residential building in Kharkiv is being cleared following a Russian ballistic missile strike," Zelenskyy said on social media.
"It was a horrible strike," a "massive strike against civilians" on "an ordinary high-rise building" that killed at least 10 people, including a 13-year-old girl and a 9-year-old boy, he said, adding that rescue teams were scouring the rubble for bodies.
"Russia has not abandoned its attempts to destroy Ukraine's residential and critical infrastructure," Zelenskyy added, urging the country's allies to continue providing military support.
The Ukrainian leader said he informed French President Emmanuel Macron about the consequences of the attacks during a phone conversation.
During the call, Zelenskyy said it was important that a 90-billion euro ($105-billion) EU aid package, as well as the next round of sanctions against Russia, currently blocked by Hungary, "are implemented."
Russia said it had carried out a "massive high-precision strike" against military targets in Ukraine. It routinely denies targeting civilian infrastructure.
The Russian army said earlier it had intercepted over 120 Ukrainian drones overnight.
The Moscow-installed authorities of Ukraine's occupied Kherson region said one person was killed and four were wounded in a Ukrainian drone strike.
An air raid alert was triggered during the night across the entire country.
The Polish air force said on X it had scrambled military aircraft to protect its airspace in regions bordering Ukraine, as it usually does in the event of large-scale Russian strikes.
One person died in Ukraine's eastern region of Dnipropetrovsk and three were wounded in the capital Kyiv, authorities said.
In the Sumy region bordering Russia, a 24-year-old man died in his car when it was hit by a Russian drone, according to local officials.
The drone barrages from either side follow on the heels of an exchange between Moscow and Kyiv of 500 prisoners of war each, in line with accords reached during the latest round of peace talks in Geneva.
Negotiations appeared to have stalled amid a lack of progress and since the eruption of war in the Middle East.
Zelenskyy earlier warned that a prolonged Middle East conflict could hinder deliveries of U.S.-made air defense missiles.
Ukraine is facing a shortage of expensive U.S. PAC-3 air defense ammunition.
Zelenskyy has offered to the United States an exchange of Ukraine's drone interceptors for the missiles.
He has also suggested sending drone specialists to help shield Washington's Gulf allies from Iranian drones.
A delay in U.S. missile supplies during winter made Ukraine's civil infrastructure more vulnerable to widespread Russian airstrikes that left hundreds of thousands without heating in freezing temperatures.
