Ukrainian servicemen stand next to a fragment of a Tochka-U missile in Kramatorsk, Ukraine. AP

Zelensky's voice rose in anger during his nightly address late on Friday, when he said the strike on the Kramatorsk train station, where 4,000 people were trying to flee a looming Russian offensive in the east, amounted to another war crime.

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Russia denied it was responsible for the strike. Among those killed were children, and dozens of people were severely injured.

Photos taken after the attack showed corpses covered with tarpaulins, and the remnants of a rocket painted with the words "For the children" in Russian. The Russian phrasing seemed to suggest the missile was sent to avenge the loss or subjugation of children, although its exact meaning remained unclear.

A man walks past burned cars at the site of a missile strike at a rail station in Kramatorsk, Ukraine. Reuters

The strike seemed to shock world leaders.

"There are almost no words for it,” European Union Commission President Ursula von der Leyen told reporters during a visit to Ukraine. "The cynical behavior (by Russia) has almost no benchmark anymore.”

The attack came as workers elsewhere in the country unearthed bodies from a mass grave in Bucha, a town near Kyiv, where graphic evidence of dozens of killings emerged following the withdrawal of Russian forces.

"Like the massacres in Bucha, like many other Russian war crimes, the missile attack on Kramatorsk should be one of the charges at the tribunal that must be held,” Zelensky said.

Associated Press