A massive Russian drone and missile strike has wounded at least 20 people in Kyiv, plunging Ukraine’s capital into darkness early on Friday in what Volodomyr Zelenskyy condemned as a “cynical and calculated” attack.

Kyiv’s mayor, Vitali Klitschko, said Russian forces had targeted “critical infrastructure”, and fragments from downed drones struck several parts of the city. Images posted online showed firefighters working to tackle burning blocks of flats.

The Ukrainian air force said the overnight Russian barrage comprised 465 drones and 32 missiles, and that its air defence systems downed 405 and 15 of them respectively.

In the heart of Kyiv, rescuers pulled more than 20 people out of a 17-storey block of flats as flames engulfed the sixth and seventh floors. Five people were taken to hospital, while others received first aid at the scene, authorities said.

Elsewhere in Ukraine, a seven-year-old child was killed in Russian strikes in the south-east.

President Zelenskyy said the main target had been Ukraine’s energy infrastructure as temperatures begin to drop.

“It is precisely the civilian and energy infrastructure that is the main target of Russia’s strikes ahead of the heating season,” Zelenskyy said in a post on X as he called for more support from Kyiv’s allies.

“What’s needed is not window dressing but decisive action – from the United States, Europe, and the G7 – in delivering air defence systems and enforcing sanctions.”

Zelenskyy warned on Thursday that Moscow was seeking to “create chaos and apply psychological pressure” by damaging energy facilities and railways. The Ukrainian private energy firm DTEK said its thermal power plants had suffered significant damage in the attack but did not immediately provide further details.

The Kremlin has escalated aerial attacks on Ukrainian energy facilities and rail systems in recent weeks, escalating bombing campaigns it carried out over the previous three winters that left people without heating in frigid temperatures.

Urging people in Kyiv to remain in shelters, the Ukrainian air force said: “The capital of the country is under an enemy ballistic missile attack and a massive attack by the enemy strike drones.”

The prime minister, Yulia Svyrydenko, said the assault was among the heaviest concentrated strikes on energy infrastructure since the war began and reported significant damage.

Firefighters work to extinguish fires in a block of flats in Kyiv after the Russian attack. Photograph: Ukrainian State Emergency Service/AFP/Getty Images

Around 28,000 families in the Kyiv region remained without power on Friday morning, the governor, Mykola Kalashnyk, said.

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“As soon as safety conditions allow, energy experts will begin clarifying the consequences of the attack and conducting restoration work.”

Russia also hit the south-eastern region of Zaporizhzhia with at least seven overnight drone strikes, killing a seven-year-old and wounding at least three people, according to Ivan Fedorov, the head of the regional military administration.

Zelenskyy has said Russian attacks this year have already strained Ukrainian gas infrastructure, and more strikes could force his country to increase imports.

Ukraine has also stepped up its drone and missile strikes on Russian territory, a tactic that Zelenskyy said was showing “results” and pushing up fuel prices in Russia.

A Ukrainian hit on a power station in the Russian border region of Belgorod also caused outages.

Russia accused Ukraine on Thursday of rupturing a now defunct pipeline near the frontline used to transport ammonia into Ukraine for export, releasing toxic gas. It posted a video showing what appeared to be clouds of a chemical compound spewing from a source in the ground.

Authorities in Ukraine’s eastern Donetsk region said the incident did not present a “menace to the lives of people” living nearby.

Reuters and Agence France-Presse contributed to this report