Russian forces have been accused of trucking Ukrainian bodies to a mass burial area that has allegedly been dug on the outskirts of Mariupol as Vladimir Putin claimed victory in the city.

Satellite images from Maxar Technologies are purported to show four such grave sites that have been expanding over the last few weeks.

Mariupol’s mayor Vadym Boichenko and his adviser have both publicly alleged the Russians have been collecting the city’s dead from the streets and dumping the bodies at the mass grave site.

It comes as Russian President Vladimir Putin cancelled plans to storm the last Mariupol stronghold where hundreds of Ukrainians are holding out in the Azovstal steelworks.

Instead Mr Putin ordered the industrial area to be sealed off “so a fly cannot get through” as he claimed victory in the biggest battle of the war, declaring Mariupol “liberated” after nearly two months of bombardment.

Revealing the location of the alleged grave site, the mayor of Mariupol’s adviser said it had been identified after a lengthy search amid claims up to 20,000 Ukrainians have died in the port city.

“As a result of a long search and identification of places of mass burial of dead Mariupol residents, we established the fact of arrangement and mass burial of the dead Mariupol residents in the village of Manhush,” wrote Petro Andriushchenko.

“Trucks carry in the bodies of the dead, in fact, simply dumping them on the embankment.

“This is direct evidence of war crimes and attempts to cover them up.”

The mayor said: “There is a field near the cemetery, and in this field there are ditches, 30 metres (about 90 feet) long, and there they bury them, bring the bodies of the dead by trucks and throw them into these ditches.”

Satellite images of the cemetery in Manhush, some 20 kilometres west of Mariupol. Photo: Maxar Technologies

Maxar Technologies published satellite imagery which it said was evidence of new graves at a site.

“According to recent media reports, Russian soldiers have been taking the bodies of people killed in Mariupol to this location,” the Maxar analysis said.

“A review of our satellite images from mid-March through mid-April indicate that the expansion of the new set of graves began between March 23-26, 2022 and has continued to expand over the past couple of weeks.

“The graves are aligned in four sections of linear rows (measuring approximately 85 metres per section) and contain more than 200 new graves.”

Russian/ pro-Russian armour gathers in eastern Mariupol for an assault on the Azovstal steel plant. Photo: Getty

Meanwhile Ukraine’s military intelligence said it had intercepted Russian communications which exposed an alleged order to kill Ukrainian prisoners of war in the city of Popasna in the eastern region of Luhansk.

“The Main Intelligence Directorate of the Ministry of Defence of Ukraine received an audio interception of the occupiers’ conversation, which refers to the order to kill all prisoners of war of the Armed Forces of Ukraine who are in their captivity in the area of Popasna (Luhansk Region),” Ukrainian military intelligence tweeted.

“This is a blatant war crime, a violation of international law, and another striking example that the Russian military are murderers, rapists, and looters.”

Russia has said it has entered a new stage of its operation and is methodically seeking to “liberate” the Donbas region of eastern Ukraine.

Biden: War at ‘critical window’

As Ukraine faces a fresh onslaught from Russia on its eastern flank, US President Joe Biden announced another $US800 million ($1.1 billion) security assistance package.

Mr Biden pledged to send dozens of howitzers, 144,000 rounds of ammunition and tactical drones as he called on Congress for to provide additional aid for Ukraine.

“We’re in a critical window now of time where they’re going to set the stage for the next phase of this war,” Mr Biden said.

He said the US and allies were “moving as fast as possible” to provide Ukraine with the equipment and weapons it needed.

The US House of Representatives will consider the additional aid for Ukraine as soon as next week, Speaker Nancy Pelosi told reporters.

There is strong support among Democrats and Republicans for assisting Ukraine.

The president also announced plans to ban Russian-affiliated ships from US borders, further ratcheting up pressure on officials in Moscow.

The new arms package is the same size as one announced last week.

US officials anticipate Russia’s campaign could last many months, grind to a stalemate and test the battlefield capabilities of Ukrainian fighters.

-with AAP