(MARIUPOL, Ukraine) — In one of the creepiest allegations to emerge from the Russian invasion of Ukraine, the Kremlin is being accused by Ukrainian officials of using “mobile crematoriums” to incinerate dead civilians in a deliberate effort to cover-up alleged war crimes in the hard-hit city of Mariupol.

Mariupol Mayor Vadym Boychenko made the charge this week, saying he heard eyewitness accounts of Russian soldiers driving around Mariupol with crematoriums on lorries and collecting bodies of civilians while at the same time barring the International Committee of the Red Cross from entering the city with humanitarian aid.

“The world has not seen the scale of the tragedy in Mariupol since the existence of Nazis concentration camps,” Boychenko said on Tuesday. “The Russians have turned our entire city into a death camp. Unfortunately, the creepy analogy is getting more and more confirmation.”

In a statement released on its Facebook account, the Mariupol City Council said, “witnesses have seen evidence Russia is operating mobile crematoria in Mariupol, burning the bodies of dead civilians and covering up evidence of war crimes.”

The statement added “this is why Russia is not in a hurry” to let the ICRC and other human rights watch groups into Mariupol to rescue civilians still trapped there.

Boychenko and the city council said the portable human furnaces showed up in Mariupol after reports of alleged atrocities at the hands of Russian troops emerged in Bucha, a suburb of the capital city Kyiv. Ukrainian officials reported that at least 410 civilians were killed in Bucha, including many found with their hands tied behind their backs and shot in the head.

Boychenko said his once-thriving port city of 400,000 people has been completely decimated by bombing raids and estimated that around 5,000 people there have been killed.

U.S. defense officials told ABC News they have not confirmed the allegations that Russia is using mobile crematoriums to hide evidence of war crimes.

Rep. Seth Moulton, D-Massachusetts, told ABC News on Thursday that he is not surprised by the reports.

Moulton, a former Marine and a member of the House Armed Services Committee, said that during a 2015 fact-finding mission in Ukraine that he went on with other House members, “credible sources” informed him that the Russian Army was using mobile crematoriums on its own soldiers in the Russian occupied Crimea, Ukraine. He said the sources told him Russia was using the devices to cover up the number of its soldiers killed in Crimea.

“We heard this from a variety of sources over there, enough that I was confident in the veracity of the information,” Moulton said. “None of that has changed. That is absolutely what was going on back then and I’m now hearing reports, unsurprisingly, that it’s happening again.”

Moulton said he has no reason to discounts reports from Ukrainian officials that Russia is using the incinerators to hide new war crimes.

“The bottom line is this is nothing new for the Russian Army and Vladimir Putin,” Moulton said.

In an interview with Turkish media this week, Ukrainian President Volodymyr Zelenskyy alleged that Russian soldiers were “cleaning up” before allowing aid workers into the heavily bombed Mariupol.

Pressure has been mounting from the international community to bring war crimes against Putin and other Russian officials. The international criminal court in The Hague has launched an investigation into the atrocities allegedly committed against Ukrainian civilians by Russian troops since the invasion started on Feb. 24.

A report released Thursday by Amnesty International claims Russian forces have committed numerous war crimes throughout Ukraine. The organization said its crisis response investigators interviewed more than 20 people from villages and towns near Kyiv and many claimed to have witnessed civilian executions.

The United Nations General Assembly on Thursday voted to pass a resolution to suspend Russia from the U.N. Human Rights Council in response to Russian forces’ alleged killings of civilians in Ukraine.

“I’m not sure who needs more proof that Russia is committing war crimes,” Moulton told ABC News. “They’re trying to cover their tracks.”

Russia has denied committing atrocities and targeting civilians.

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