Kyiv mourns 30 killed in Russian attack

Rescuers cleared the rubble in the Ukrainian capital Kyiv in a search for survivors on Friday, as flags were lowered to half mast to mark a day of mourning, a day after a Russian missile and drone attack killed at least 30 people.

Thursday's attack - the deadliest Russian strike on Ukraine's capital this year - also injured 92 people, Kyiv Mayor Vitali Klitschko said. 

The parents of a 10-year-old boy, who was hospitalised after the attack, as well as a 15-year-old girl were still unaccounted for, he said.

Separately, a Russian drone attack on a house in the northern Sumy region killed four people overnight on Friday, including a woman and her toddler daughter, the Prosecutor General's Office said.

Klitschko announced a day of mourning in Kyiv for Friday.

Rescue operations were continuing for a second day, he said, as forensic experts worked to identify body parts.

In recent months, Ukraine has slowed Russian advances to a crawl on the 1200-km front line, and has retaken territory in some areas.

"Russia has no argument left for its war other than its ballistic missiles," Ukrainian President Volodymyr Zelenskiy said in his evening address on Thursday.

"(Russian President Vladimir) Putin still intends to 'vanquish' residential buildings rather than end this war."

The scale and spread of destruction across the breadth of the capital had little precedent even in a war now in its fifth year.

Zelenskiy said more than 100 residential buildings had been damaged.

Moscow said the attacks were retaliation for Ukrainian drone strikes on Russia.

After years of enduring long-range attacks from Russia, Ukraine has intensified its own strikes deep into Russian territory, mainly on energy targets. That has triggered a fuel crisis in Russia, forcing the world's third-biggest oil producer to import gasoline.

Russia has responded with a stepped-up air campaign against Ukrainian cities, last month hitting a 1000-year-old Kyiv cathedral foundational to the Orthodox faith in both countries.