Christians have been called to pray fervently for an end to the war in Ukraine. The plea comes as Western officials accused their Russian counterparts of war crimes on Friday after Russian missiles struck a Ukrainian city far behind the frontlines.

Kyiv officials said the attack killed at least 23 people.

Ukraine said Thursday's strike on Vinnytsia, a city of 370,000 people about 200 km (125 miles) southwest of Kyiv, had been carried out with Kalibr cruise missiles launched from a Russian submarine in the Black Sea.

The attack was the latest in a series of Russian strikes in recent weeks using long-range missiles on crowded buildings in cities far from the front, each killing dozens of people.

Russia, which denies targeting civilians, said the building it struck on Thursday was used to train troops. Ukraine said it was an office building housing a cultural centre used by retired veterans.

President Volodymyr Zelenskiy called Russia a terrorist state, urged more sanctions against the Kremlin and said the death toll in Vinnytsia could rise.

"Unfortunately, this is not the final number. Debris clearance continues. Dozens of people are reported missing. There are seriously injured (people) among those hospitalised," he said in a video address.

Zelenskiy told an international conference aimed at prosecuting war crimes in Ukraine that the attack had been mounted on "an ordinary, peaceful city".

"No other state in the world poses such a terrorist threat as Russia," Zelenskiy said.

Christian political commentator Martyn Whittock told Premier, Russia has created a vicious cycle of violence.

"What we're particularly seeing here, in the latest of these appalling attacks on Ukrainian cities far from the front line, we're seeing the Russians effectively demonstrate their reach, they are saying this can go on, this will go on, and we have the capability to do this.

"The more this goes on, the less likely Ukrainians are to actually come to terms because of the appalling civilian casualties that are being inflicted upon them. 

"Ukrainians are just not prepared, understandably, to see recede territory at all. Because they're saying effectively, you are committing a war crime after war crime, and we're simply not going to deal with you. So it's counterproductive. But then that seems to produce yet another round of Russian extreme violence in order to try to force the Ukrainians to the table. So it is it's a shocking cycle of violence."

Ukraine's state emergency service said three children, including a 4-year-old girl, were killed in Thursday's attack. Another 71 people were hospitalised and 29 people were missing.

It posted a photograph on its Telegram channel of a toy kitten, a toy dog and flowers lying in the grass. "The little girl Lisa, killed by the Russians today, has become a ray of sunshine," it said. Images of the girl, who had Down's Syndrome, pushing a pram like one found in the debris, went viral online.

Authorities in the southern city of Mykolaiv, closer to the frontlines, reported fresh Russian strikes on Friday morning, which wounded at least two people.

Whittock has urged Christian to not be desensitised to the war as time goes by and to continue praying. 

"We must be praying for transformation of hearts at the heart of Russian government. There must be people around Putin who are beginning to think, even if not from the best humanitarian motives, this cannot go on the way it is going on. 

"And there must be changed within the heart of Russia leadership, we must pray for transformation within the heart and mind of Vladimir Putin. But we must also pray that those around him will finally have the courage, even in the middle of a war, which is not an easy thing to do to change tactics and say 'we will not put up with this, we must stop this'.

"We will be praying for that miraculous transformation because unless it changes at the top, it's difficult to see this not going on and on and turning into almost a forever war, as these things are sometimes termed."

More than 40 countries agreed on Thursday to coordinate investigations into suspected war crimes.