Ukrainian President Volodymyr Zelenskyy said he wants a tough global response to Russia after its forces fired a missile at a crowded train station, killing at least 52 people.

Zelenskyy's voice rose in anger during his nightly address late 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.

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.

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,” Zelenskyy said.

He said efforts would be taken “to establish every minute of who did what, who gave what orders, where the missile came from, who transported it, who gave the command and how this strike was agreed to.”

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After failing to take Kyiv in the face of stiff resistance, Russian forces have now set their sights on the eastern Donbas region, the mostly Russian-speaking, industrial area where Moscow-backed rebels have been fighting Ukrainian forces for eight years and control some places.

Although the train station is in Ukrainian government-controlled territory in the Donbas, Russia accused Ukraine of carrying out the attack. So did the region’s Moscow-backed separatists, who work closely with Russian troops.

Western experts, however, dismissed Kremlin spokesperson Dmitry Peskov's assertion that Russian forces “do not use” that type of missile. A Western official, speaking on condition of anonymity to discuss intelligence, said Russia’s forces have used the missile — and that given the strike’s location and impact, it was likely Russia’s.

Justin Bronk, a research fellow at the Royal United Services Institute in London, added that only Russia would have reason to target railway infrastructure in the Donbas, as it is critical for the Ukrainian military's efforts to reinforce its units.

Bronk pointed to other occasions when Russian authorities have tried to deflect blame by claiming their forces no longer use an older weapon “to kind of muddy the waters and try and create doubt.” He suggested Russia specifically chose the missile type because Ukraine also possesses them.

British Defense Minister Ben Wallace denounced the attack as a war crime, and U.N. Secretary-General Antonio Guterres called it “completely unacceptable.”

Ukrainian authorities and Western officials have repeatedly accused Russian forces of atrocities in the war that began with a Feb. 24 invasion. More than 4 million Ukrainians have fled the country, and millions more have been displaced. Some of the grisliest evidence has been found in towns around Ukraine's capital, Kyiv, from which Russian President Vladimir Putin's troops pulled back in recent days.

In Bucha, Mayor Anatoliy Fedoruk has said investigators found at least three sites of mass shootings of civilians and were still finding bodies in yards, parks and city squares — 90% of whom were shot.

Russia has falsely claimed that the scenes in Bucha were staged.

On Friday, workers pulled corpses from a mass grave near a church under spitting rain, lining up black body bags in rows in the mud. About 67 people were buried there, according to a statement from Prosecutor-General Iryna Venediktova's office.

Zelenskyy cited communications intercepted by the Ukrainian security service as evidence of Russian war crimes, in an excerpted interview with CBS' “60 Minutes” that aired Friday.

“There are (Russian) soldiers talking with their parents about what they stole and who they abducted. There are recordings of (Russian) prisoners of war who admitted to killing people,” he said. “There are pilots in prison who had maps with civilian targets to bomb. There are also investigations being conducted based on the remains of the dead.”

Zelenskyy's comments echo reporting from German news magazine Der Spiegel saying Germany's foreign intelligence agency had intercepted Russian military radio traffic in which soldiers may have discussed civilian killings in Bucha. The weekly also reported that the recordings indicated the Russian mercenary Wagner Group was involved in atrocities there.

German government officials would not confirm or deny the report, but two former German ministers filed a war crimes complaint Thursday. Russia has denied that its military was involved in war crimes.

Elsewhere, in anticipation of intensified attacks by Russian forces, hundreds of Ukrainians fled villages that were either under fire or occupied in the southern regions of Mykolaiv and Kherson.

Ukrainian officials have almost daily pleaded with Western powers to send more arms, and to further punish Russia with sanctions, exclusion of Russian banks from the global financial system and a total EU embargo on Russian gas and oil.

NATO nations agreed Thursday to increase their supply of weapons, and Slovakian Prime Minister Eduard Heger announced on a trip to Ukraine on Friday that his country has donated its Soviet-era S-300 air defense system to Ukraine. Zelenskyy had appealed for S-300s to help the country “close the skies” to Russian warplanes and missiles.

A senior U.S. defense official said Friday that the Pentagon believes some of Russia's retreating units were so badly damaged they are “for all intents and purposes eradicated.” The official spoke on condition of anonymity to discuss internal military assessments.

The official said the U.S. believes Russia has lost between 15% and 20% of its combat power overall since the war began. While some combat units are withdrawing to be resupplied in Russia, Moscow has added thousands of troops around Ukraine’s second-largest city, Kharkiv, he said.

In Kharkiv, Lidiya Mezhiritska stood in the wreckage of her home after overnight missile strikes turned it to rubble.

“The ‘Russian world,’ they say,” she said, wryly invoking Putin’s nationalist justification for invading Ukraine. “People, children, old people, women are dying. I don’t have a machine gun. I would definitely go (fight), regardless of age.”