A large-scale overnight drone and missile attack on the Ukrainian capital killed at least 10 people.
It injured more than 50 and damaged residential buildings across the city.
Russia said the strikes targeted military and energy infrastructure in response to recent Ukrainian attacks on Russian civilian infrastructure.
Russian forces launched a large-scale drone and missile attack on the Ukrainian capital Kyiv early on Thursday, killing at least 10 people and injuring more than 50 after strikes hit residential areas. Moscow said the assault was retaliation for recent Ukrainian attacks on Russian civilian infrastructure.
Ukrainian President Volodymyr Zelenskyy had earlier warned of a possible overnight attack and said he was cutting short his visit to Dublin for the start of Ireland's six-month term in the rotating presidency of the EU.
Kyiv Mayor Vitali Klitschko said on Telegram that 10 people were killed. A direct hit by a Russian projectile partially collapsed six floors of an apartment building.
Reuters video showed emergency workers searching through the rubble of what had been a nine-storey residential building as dawn broke over the capital, while fires burned across several parts of the city.
Tymur Tkachenko, head of Kyiv's military administration, said 56 people, including two children, were injured and that attacks damaged three dozen locations across the city.
"The enemy has once again deliberately targeted residential neighbourhoods and killed civilians. We have sustained extensive damage and a significant number of casualties, including children," he wrote on Telegram.
Klitschko said earlier that the injured included paramedics and drivers at an ambulance station, while some residents remained trapped inside damaged apartment buildings.
Air raid alerts were issued across most of Ukraine overnight, sending residents into underground metro stations with children, personal belongings, tents and pets during what Ukrainian officials described as Russia's heaviest attack since mid-June.
"Do not delay decisions on air defence for Ukraine! This is our main request to our partners after Kyiv suffered a night of horror," Ukrainian Foreign Minister Andrii Sybiha said on X while visiting Japan on Thursday.
Poland, a NATO and European Union member, briefly deployed fighter jets as a precaution during the attack before later standing them down after confirming that its airspace had not been violated. Finland also temporarily established a restricted aviation zone over the eastern Gulf of Finland before lifting the measure later, its defence forces said on X.
Russia's Defence Ministry said on Telegram that its "massive attack", involving long-range precision weapons launched from the air, land and sea, along with drones, targeted military facilities, energy infrastructure and airports in Kyiv and other locations.
The ministry said the strikes were retaliation for Ukrainian attacks on Russian civilian infrastructure, without providing further details. It also said Russian air defences shot down 327 drones overnight, including those intercepted over Russian-occupied parts of Ukraine.
The attack came as Zelenskyy has proposed talks with Russian President Vladimir Putin to end the more than four-year-old war, an offer the Kremlin leader has rejected.
Ukraine has recently stepped up long-range strikes inside Russia, contributing to a fuel crisis in the world's third-largest oil producer and forcing Moscow to import petrol from as far away as India.
Novosibirsk Governor Andrey Travnikov said on Telegram that fuel shortages were worsening in the region, located more than 3,000 km (1,860 miles) east of Moscow, and that emergency services would receive priority for supplies.
