The mayor of the besieged port city of Mariupol put the number of civilians killed there at more than 5,000 Wednesday, as Ukraine collected evidence of Russian atrocities on the ruined outskirts of Kyiv and braced for what could become a climactic battle for control of the country’s industrial east.

Ukrainian authorities continued gathering up the dead in shattered towns outside the capital amid telltale signs Moscow’s troops killed civilians indiscriminately before retreating over the past several days.

In other developments, the U.S. and its Western allies moved to impose new sanctions against the Kremlin over what they branded war crimes.

And Russia completed the pullout of all of its estimated 24,000 or more troops from the Kyiv and Chernihiv areas in the north, sending them into Belarus or Russia to resupply and reorganize, probably to return to the fight in the east, a U.S. defense official speaking on condition of anonymity said.

In his nightly address, Ukrainian President Volodymyr Zelenskyy warned that the Russian military continues to build up its forces in preparation for the new offensive in the east, where the Kremlin has said its goal is to “liberate” the Donbas, Ukraine’s mostly Russian-speaking industrial heartland. He said Ukraine, too, was preparing for battle.