More than 5,000 people have been killed in the Ukrainian city of Mariupol and around 90 per cent of the city's infrastructure has been destroyed in the Russian siege of the city, said Vadym Boichenko, the city's mayor, on Wednesday.

The dead include 210 children.

Boichenko said these people have been killed in weeks of Russian bombardment and street fighting. He added that Russians have bombed hospitals, including one where 50 people burned to death.

The punishing attacks on the strategic port on the Sea of Azov have cut off food, water, fuel and medicine and pulverized homes and businesses, according to Boichenko.

British defense 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.

Capturing the city would allow Russia to secure a continuous land corridor to the Crimean Peninsula, which Russia seized from Ukraine in 2014.

As Russians withdraw from other parts of Ukraine to focus on the country's east, Ukrainians have been collecting evidence of Russian atrocities on the outskirts of Kyiv. Ukrainian authorities are gathering up the dead in ruined towns outside the capital amid telltale signs that Russian troops killed civilians indiscriminately before retreating over the past several days.

Russia has 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, a US defense official speaking on condition of anonymity said.

Meanwhile, in the scarred and silent streets of Bucha and other towns around Ukraine's capital where Russian forces withdrew, investigators sought to document what appeared to be widespread killings of civilians. Some victims had evidently been shot at close range. Some were found with their hands bound or their flesh burned.

At a cemetery in Bucha, workers began to load more than 60 bodies apparently collected over the past few days into a grocery shipping truck for transport to a facility for further investigation.?

More bodies were yet to be collected in Bucha. The Associated Press saw two in a house in a silent neighborhood. From time to time there was the muffled boom of workers clearing the town of mines and other unexploded ordnance.

In Andriivka, a village about 60 kilometers (40 miles) west of Kyiv, two police officers from the nearby town of Makariv came Tuesday to identify a man whose body was in a field beside tank tracks. Officers found 20 bodies in the Makariv area, Capt. Alla Pustova said.

Andriivka residents said the Russians arrived in early March and took locals' phones. Some people were detained, then released. Others met unknown fates. Some described sheltering for weeks in cellars normally used for storing vegetables for winter.

Ukrainian authorities have said the bodies of at least 410 civilians have been found in towns around Kyiv, and Associated Press journalists in Bucha counted dozens of corpses in civilian clothes and interviewed Ukrainians who told of witnessing atrocities.?

In a video address Tuesday to the UN Security Council, Ukrainian President Volodymyr Zelenskyy said that civilians had been raped, tortured, shot in the back of the head, thrown down wells, blown up with grenades in their apartments and crushed to death by tanks while in cars.?

Elsewhere in Ukraine, the aid group Doctors without Borders said its staff witnessed an attack Monday on a cancer hospital in a residential district of the southern city of Mykolaiv. The group said it was the third known strike in recent days on a hospital in the port city, whose capture is key to giving Russia control of the Black Sea coast. It said it had no overall death toll, but its team saw one body.?

Ukrainian President Volodymyr Zelenskyy warned that Moscow is now marshaling 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,” Zelenskyy 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.

With AP inputs