Russia fired its biggest-ever aerial barrage at Ukraine early on Sunday, killing at least two people and setting the seat of the Ukrainian government in Kyiv ablaze, authorities said.

Witnesses saw the roof of Ukraine's cabinet of ministers in flames and smoke billowing over the capital.

Drone strikes also damaged several high-rise buildings in Kyiv, according to emergency services.

The barrage came after several European countries, led by France and Britain, pledged on Thursday to deploy "reassurance" forces to Ukraine to patrol a peace deal between the warring sides – a demand Moscow has deemed unacceptable.

The attack on Ukraine's cabinet of ministers, a sprawling government complex at the heart of Kyiv, was the first such strike of the war.

"The roof and upper floors were damaged due to an enemy attack. Rescuers are extinguishing the fire," Prime Minister Yulia Svyrydenko said on Telegram.

"We will restore the buildings. But we cannot bring back lost lives. The enemy terrorises and kills our people every day throughout the country," she said.

Russia fired at least 805 drones and 13 missiles at Ukraine between late Saturday and early Sunday, in a new record, according to the Ukrainian air force.

Ukrainian President Volodymyr Zelensky said emergency services were working across the country.

A strike on a nine-storey residential building in the west of Kyiv killed at least two people, a mother and her two-month-old son, prosecutors said. (AFP)