The number was given on Wednesday as Ukraine collected evidence of Russian atrocities on the 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 ruined towns outside the capital amid telltale signs that Moscow's troops killed civilians indiscriminately before retreating over the past several days.
Mariupol Mayor Vadym Boichenko said that of the more than 5000 civilians killed during weeks of Russian bombardment and street fighting, 210 were children.
He said Russian forces bombed hospitals, including one where 50 people burned to death.
Russia has completed the withdrawal 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 reorganise, a US defence official, speaking on condition of anonymity, said on Wednesday.
Ukrainian President Volodymyr Zelenskiy warned Moscow is marshalling reinforcements and trying to push deeper into the country's east, where the Kremlin has said its goal is to "liberate" the Donbas, Ukraine's mostly Russian-speaking industrial heartland.
"The fate of our land and of our people is being decided. We know what we are fighting for. And we will do everything to win," Zelenskiy said.
Ukrainian authorities urged people living in the Donbas to evacuate now, ahead of an impending Russian offensive, while there is still time.
"Later, people will come under fire," Deputy Prime Minister Iryna Vereshchuk said.
'And we won't be able to do anything to help them."
A Western official, speaking on condition of anonymity to discuss intelligence estimates, said it will take Russia's damaged forces as much as a month to regroup for a major push on eastern Ukraine.
Almost a quarter of its battalion tactical groups in the country have been rendered "non-combat-effective" and have either withdrawn or merged with other units, the official said.
Mayor Boichenko said that more than 90 per cent of the city's infrastructure has been destroyed.
The punishing attacks on the strategic port on the Sea of Azov have cut off food, water, fuel and medicine and pulverised homes and businesses.
British defence officials said 160,000 people remained trapped in the city, which had a pre-war population of 430,000.
A humanitarian-relief convoy accompanied by the Red Cross has been trying without success to get into the city since Friday.