BSS/AFP) - Russian strikes across Ukraine overnight killed at least two people and wounded dozens more, authorities said, as a nationwide air alert was declared.

The State Emergency Service said an attack on the capital Kyiv had damaged several high-rise buildings, and shared photos of firefighters battling a blaze on an elevated floor.

"One person died and 18 others were wounded in the capital as a result of the massive attack," the service said on Telegram.

"The fires have been contained, and emergency rescue operations are ongoing," it said.

Ukrainian authorities declared a nationwide air alert at 6:06 am (0306 GMT).

Another strike in the northeastern Sumy region killed one person and wounded several more, local authorities said late on Saturday.

"Following an enemy attack on the outskirts of the town of Putyvyl, one person has died, and there are people injured," including a nine-year-old child, said regional military governor Oleg Grygorov on Telegram.

A Russian drone attack on Saturday evening in Zaporizhzhia in the southeast wounded at least 15 people, four of whom were hospitalised, said Ivan Fedorov, the head of the military administration in the region, which is partially occupied by Russia.

He published images of shattered residential buildings.

Russian forces occupy around 20 percent of Ukrainian territory in total.

The barrage came after two dozen countries, led by France and Britain, pledged Thursday to join a "reassurance" force to patrol any agreement to end the war, unleashed by Moscow`s February 2022 invasion.

However, Russian President Vladimir Putin has dismissed any Western forces in Ukraine as unacceptable and said they would be "legitimate" targets.

Efforts in recent weeks by US President Donald Trump to end the three-and-a-half-year war have so far yielded little progress.