At least 52 people were killed in a missile strike on a train station in Ukraine's eastern province.
Authorities said five children were among those killed in the attack which took place in Kramatorsk, the capital of Donetsk.
President Volodymyr Zelensky said at least 300 people were wounded as he called for "a firm global reaction to this war crime". France called it a "crime against humanity" as President Biden said it was a "horrific atrocity".
Regional governor Pavlo Kyrylenko said that the station was hit by a Russian Tochka U short-range ballistic missile. The White House said it was open to supporting an investigation intothe Kramatorsk attack even as UK PM Boris Johnson said: "the depths to which Putin's vaunted army has sunk".
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The latest strike comes amid allegations that Russian troops executed civilians in Bucha with mass graves being found in the town. Russia denied it was responsible for the killings.
The war in Ukraine has been going on for over six weeks with Ukraine's cities being bombed by Russian forces. President Putin had announced a "special military operation" on February 24 against Ukraine.
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Reports claim over 4 million people have fled Ukraine into neighbouring EU countries even as talks continue between Ukraine and Russia. Meanwhile, the US extended export curbs on Russia and Belarus putting curbs on fertilizer and pipe valves.
EU foreign policy chief Josep Borrell said the possibility of an oil ban would be discussed even though European nations are heavily dependent on Russian energy.
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Reports said Slovakia has donated the S-300 air defence system to Ukraine with the British government ready to send another $130 million worth of military support to Ukraine.
(With inputs from Agencies)