Officials say a Russian missile and drone bombardment has killed at least 15 people and injured 156 others in Ukraine overnight, with the main barrage demolishing a nine-story apartment building in Kyiv.

It was the deadliest attack on the Ukrainian capital in almost a year, and came as Moscow has intensified air assaults on the city.

Earlier, Kyiv mayor Vitali Klitschko said on his Telegram channel that a 62-year-old American was found dead in a house opposite where medics were providing assistance to victims of Russia's overnight strike. At least 16 people were killed and 124 others were wounded in the attacks.