Russia launched large-scale drone and missile strikes on Ukraine's capital and other parts of the country early on Friday, officials said.
At least three people were killed and 49 injured in the strikes, according to Ukraine's President Volodymyr Zelensky.
The aerial raids targeted Kyiv, as well as the city of Lutsk and the Ternophil region in the north-west of the country.
The attack came after Russian President Vladimir Putin warned US President Donald Trump he would respond to Ukraine's recent strikes on Russian airbases.
"As of now, three deaths have been confirmed - all of them were employees of the State Emergency Service of Ukraine," Zelensky said.
He said the attack used more than 400 drones and more than 40 missiles, and the number of people injured "may increase".
In an earlier statement, Kyiv's Mayor Vitali Klitschko said four people had been killed in the country's capital.
Air raid alerts were in place in the capital, as well as the cities of Kharkiv, Sumy and Luhansk. Kyiv's train system was disrupted after shelling damaged metro tracks.
Outside of the capital, Ternopil's military chief Vyacheslav Negoda said Friday's strike was the "most massive air attack on our region to date".
Mayor of Ternopil, Igor Polishchuk, said five people were wounded in the attack and there was damage to homes, schools and a government facility.
In Lutsk, five people were injured in an attack using 15 drones and six missiles, according to mayor Ihor Polishchuk.
Meanwhile, the Russian defence ministry said its air defences shot down 174 Ukrainian drones overnight in parts of Russia and occupied Crimea.
The ministry said Neptune anti-ship cruise missiles were also intercepted over the Black Sea.
Russia's latest attack on Ukraine comes days after Kyiv launched its biggest long-range drone strike on at least 40 Russian warplanes at four military bases.
Zelensky said 117 drones were used in the so-called "Spider's Web" operation by the SBU security service, striking "34% of [Russia's] strategic cruise missile carriers".
Moscow had previously said that military options were "on the table" for its response to Ukraine's attack.
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