Russia mounted an intense missile and drone barrage of the Ukrainian capital overnight, killing at least four people, according to Ukrainian officials, and sending powerful explosions reverberating across the city.

The night of attacks followed a warning from Russian President Vladimir Putin, conveyed via US leader Donald Trump, that the Kremlin would hit back against Kyiv after Ukrainian drones destroyed several of Russia’s strategic bomber aircraft in coordinated attacks deep inside Russia.

Kyiv mayor Vitali Klitschko indicated the death toll of four could rise, because rescue workers were still looking for people under the rubble of buildings. He also said 20 people were injured, of whom 16 were hospitalised.

Operation of the city’s metro transport system was disrupted because a Russian strike had hit and damaged a train between stations, the city’s military administration said.

The air attack also triggered fires in residential buildings in different parts of the city, authorities said.

Earlier in the night, as the attacks came in, Reuters reporters could hear the sound of Russian kamikaze drones buzzing in the sky, accompanied by the sounds of outgoing fire from Ukrainian anti-aircraft fire.

Reuters witnesses reported a series of booming explosions powerful enough to rattle windows far from the impact sites, and at least one large fire at the site of a drone hit.

Some Kyiv residents sought shelter in metro stations, or in underground car parks.

Ukraine’s air force said the city had been targeted with drones and Kalibr cruise missiles.

Tymur Tkachenko, head of Kyiv’s military administration, said drones had struck the upper floors of a high-rise apartment building and started a fire in Darnytskyi district on the east side of the city, where he said emergency power cuts were possible.

Tkachenko said a fire had also broken out in an apartment building in a western district. He said drone fragments had been spotted in three districts.

In one of the most audacious attacks of the war between Ukraine and Russia, Ukrainian spies last weekend destroyed some of Russia’s strategic bomber aircraft on the ground using quadrocopter drones hidden in wooden sheds.

Trump said after a phone conversation with Putin on Wednesday that the Kremlin was planning an unspecified response to the Ukrainian attack on Russian air bases.