A missile hit a train station in eastern Ukraine where thousands had gathered Friday, killing at least 52 and wounding dozens more in an attack on a crowd of mostly women and children trying to flee a new, looming Russian offensive, Ukrainian authorities said.

The attack, denounced by some as yet another war crime in the 6-week-old conflict, came as workers unearthed bodies from a mass grave in Bucha, a town near Ukraine's capital where dozens of killings have been documented after a Russian pullout.

Photos from the station in Kramatorsk showed the dead covered with tarps, and the remnants of a rocket painted with the words "For the children," which in Russian implied that children were being avenged by the strike, though the exact reason remained unclear. About 4,000 civilians had been in and around the station, heeding calls to leave before fighting intensifies in the Donbas region, the office of Ukraine's prosecutor-general said.

Ukrainian President Volodymyr Zelenskyy, who says he expects a tough global response, and other leaders accused Russia's military of deliberately attacking the station. Russia, in turn, blamed Ukraine, saying it doesn't use the kind of missile that hit the station - a contention experts dismissed.

Zelenskyy told Ukrainians in his nightly video address Friday that 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."

Pavlo Kyrylenko, the regional governor of Donetsk, in the Donbas, said 52 people were killed, including five children, and dozens more were wounded.

"There are many people in a serious condition, without arms or legs," Kramatorsk Mayor Oleksandr Goncharenko said, adding that the local hospital was struggling to treat everyone.

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

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

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 in the grave, according to a statement from Prosecutor-General Iryna Venediktova's office.

"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, his voice rising in anger late Friday.

He expounded on that theme in an excerpted interview with CBS' "60 Minutes" that aired Friday, citing communications intercepted by the Ukrainian security service.

"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 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.

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

A senior U.S. defense official said Friday that the Pentagon believes some of the 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.

The train station hit is in Ukrainian government-controlled territory in the Donbas, but Russia's Defense Ministry accused Ukraine of carrying out the attack. So did the region's Moscow-backed separatists, who work closely with Russian regular troops.

Western experts refuted Kremlin spokesperson Dmitry Peskov's assertion that Russian forces "do not use" that type of missile, saying Russia has used it during the war. One analyst added that only Russia would have reason to target railway infrastructure in the Donbas.

"The Ukrainian military is desperately trying to reinforce units in the area ... and the railway stations in that area in Ukrainian-held territory are critical for movement of equipment and people," said Justin Bronk, a research fellow at the Royal United Services Institute in London.

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 has it.

A Western official, speaking on condition of anonymity to discuss intelligence, also said Russia's forces have used the missile - and that given the strike's location and impact, it was "likely" Russia's.

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

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.

American and Slovak officials said the U.S. will then deploy a Patriot missile system to Slovakia.

After meeting with Zelenskyy on Friday, during which he urged the EU to impose a full embargo on Russian oil and gas, von der Leyen gave him a questionnaire that is a first step for applying for EU membership. She said the process for completing the questionnaire could take just weeks - an unusually fast turnaround; Zelenskyy quipped in English that they'd have the answers in a week.

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.

In the northeast's 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."

From The Associated Press