Russian missiles struck a Ukrainian city far behind the frontlines in an attack Kyiv officials said killed at least 23 people and constituted another war crime against civilians.

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

President Volodymyr Zelenskiy called Russia a "terrorist" state, urged more sanctions against the Kremlin and said that 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.

As Russia pressed its offensive in Ukraine's eastern Donbas region, the United States and more than 40 other countries agreed on Thursday to coordinate investigations into suspected war crimes.

Russia reiterated that it does not target civilians in what it calls its "special military operation" in Ukraine, and said its attack struck a military training facility. Reuters could not independently verify battlefield accounts.

Vinnytsia hosts the command headquarters of the Ukrainian Air Force, according to an official Ukrainian military website, a target which Russia used cruise missiles to try to hit in March, the Ukrainian air force said at the time.

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

Ukraine overshadows G20

The war in Ukraine has sent prices soaring for grains, cooking oils, fuel and fertiliser, stoking a global food crisis. Negotiators hope a deal will be signed next week.

US Treasury Secretary Janet Yellen condemned Russia's "brutal and unjust war" at the opening of a G20 meeting in Indonesia on Friday, and said Russian finance officials taking part in talks shared responsibility.

"By starting this war, Russia is solely responsible for negative spillovers to the global economy, particularly higher commodity prices," she said.

Russian officials participating in the meeting were "adding to the horrific consequences of this war through their continued support of the Putin regime", she added.

"You share responsibility for the innocent lives lost and the ongoing human and economic toll that the war is causing around the world," she said, addressing the Russian officials.

The United States took steps yesterday to facilitate Russian food and fertiliser exports by reassuring banks, shipping and insurance companies that such transactions would not breach Washington's sanctions on Moscow.

Enabling those Russian exports is a key part of attempts by the United Nations and Turkey to broker a package deal with Moscow that would unlock a blockade on the Black Sea port of Odesa to allow for shipments of Ukrainian grain.

The Kremlin has said that Russia is ready to halt what the West calls Moscow's unprovoked war of aggression if Kyiv agrees to its conditions, including formally recognising Russia's control of Crimea, annexed by Moscow in 2014, and the independence of two self-proclaimed Russian-backed statelets in eastern Ukraine.

Ukraine has repeatedly said it is unwilling to concede any territory and will take back any land lost by force.

The eastern Ukrainian town of Popasna which fell to Russian forces two months ago is now a ghost town with little sign of life.

A Reuters reporter who visited the town on Thursday found it almost deserted, with nearly all apartment buildings destroyed or heavily damaged.

Former resident Vladimir Odarchenko stood inside his damaged home and surveyed the debris strewn across the floor.

"I have no idea what I'm going to do. Where to live? I don't know," he said.

- Reuters