A Russian missile and drone attack killed at least 21 people across Ukraine overnight, including two children, marking one of Moscow's largest assaults in recent months.
An eight-year-old boy and three women pulled from the rubble of an apartment block were among 15 people killed in Dnipro, regional officials said. In the capital Kyiv, six people were killed.
President Volodymyr Zelensky said civilian infrastructure and energy facilities had been targeted across the country, with more than 100 people injured.
Russia's defence ministry said the strikes had been a response to previous Ukrainian attacks, saying in a statement that the "strike objectives" had all been achieved.
The Kremlin said on Tuesday it was carrying out the "systematic strikes" it had pledged after accusing Kyiv of a deadly attack on a student dormitory in an occupied part of eastern Ukraine in late May.
Kyiv said it had hit a Russian military unit.
"This practice will continue," Kremlin spokesman Dmitry Peskov told reporters on Tuesday, claiming the strikes were targeting Ukrainian military infrastructure.
Zelensky had warned a "massive strike" was possible in his nightly video address on Monday, and urged residents to pay special attention to air raid alerts.
On Tuesday morning, he said Russia had launched 656 strike drones and 73 missiles of various types - ballistic, cruise, and anti-ship - in the overnight attack.
"We urgently need help from the United States in supplying missiles for Patriot systems", the Ukrainian president said, referring to interception hardware used to intercept Russian missiles.
Patriot missiles have been in short supply, exacerbated by the US and Israeli war against Iran.
Since returning to power last year, US President Donald Trump has also stopped direct supplies to Ukraine, so Kyiv's European allies have been buying them from the US before sending them to Ukraine.
"The main strike was on Kyiv, where dozens of residential buildings and other purely civilian infrastructure were damaged again," Zelensky said.
Rescuers searching through the rubble of an apartment building in the central city of Dnipro where 15 people were killed recovered the bodies of an eight-year-old boy and three women, regional head Oleksandr Hanzha said, adding that another child had been killed in the blast.
The attack "essentially demolished" part of the building, Zelensky wrote on X.
More than 90 people were injured across both cities, while Kharkiv in the north-east - which also saw its energy facilities and civilian infrastructure hit - reported 10 injured, including a child.
An industrial facility was also attacked further south in Zaporizhzhia as regions across the country were targeted, the president said.
Large plumes of smoke could be seen rising from the centre of the capital early on Tuesday, where the head of its military administration warned ballistic missiles had been fired and the city's Mayor Vitaliy Klitschko urged residents to stay in shelters.
The buzz of drones could be heard between more than a dozen loud explosions as strikes made impact through the early morning.
The attack caused fires near a petrol station, a construction site, and several apartment blocks, as well as two houses, Klitschko said. Blackouts were also been reported across the city.
One Kyiv resident sheltering in the city's metro said she dreamed the war would soon end, but that she had "lost all hope".
"I'm always going to the metro... it's really scary to stay at home," the 32-year-old told the Reuters news agency.
Leonid Zmiievskyi, 71, said Ukrainians were surviving on their own: "Although aid is coming from the West, I don't think they're helping much. If international pressure were stronger, I think it would all be over sooner."
Kyiv-born Ukrainian tennis player Marta Kostyuk was emotional after winning her quarterfinal match at the French Open in Paris.
"We had another difficult night in Ukraine, especially in Kyiv where so many people died, so I want to give this match to Ukrainian people, their resilience. Glory to Ukraine!" she said.
Meanwhile, one person was killed in Russia's western Kursk region after a Ukrainian drone strike on Monday evening, according to regional governor Alexander Khinshtein.
A fire was also reported at an oil refinery in the south-western city of Krasnodar after it was hit by a drone, authorities there said.
Ukraine's military confirmed it had struck both areas and several others overnight.
Since a brief ceasefire expired in early May, Russia has launched several waves of missile and drone attacks on Kyiv, among them strikes on a block of flats that killed 24 people, including three children.
Days later, Ukraine responded with an attack on the Moscow region which Russian officials said had killed three people - which Zelensky said was "entirely justified".
Ukraine said Russia's threats were "nothing short of shameless blackmail" and urged allies to increase pressure on Moscow.
Russian President Vladimir Putin launched a full-scale invasion of Ukraine in 2022.
