As the US rolled out a new wave of financial sanctions on Wednesday, the mayor of Mariupol spoke out on how thousands of residents have been forcibly deported and sent to Russian “filtration camps” in occupied eastern Ukraine.

Residents of Ukraine’s besieged city are being separated from their families and stripped of their passports and identification cards. The number of people affected has been estimated to be nearly 31,000.

In a Telegram post Friday, Mayor Vadym Boychenko said he had “verified” that Ukrainians from the southern port city were being taken “at gunpoint” to “filtration camps.”

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The camp is said to be located in Novoazovsk – a Ukrainian border town 35 miles from Mariupol and just 9 miles from the Russian border. It is located in the Donetsk People’s Republic.

Just days before the February 24 invasion, the Russian State Duma passed a bill officially recognizing the self-proclaimed Donetsk and Luhansk People’s Republics, which was then signed by Russian President Vladimir Putin. 

Ukrainians have been at the camps for weeks and several government employees have been treated particularly harshly.

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“Filtration is very strict – fingerprints are taken, as well as biometrics. They force people to sign various documents,” he described, according to a translation by a Ukrainian news agency.

The filtration camps, are said to be large plots of military tents with rows of men in uniforms. Ukrainians are photographed, fingerprinted, forced to turn over their cellphones, passwords and identity documents.

U.S. Ambassador to the United Nations Linda Thomas-Greenfield said that she has seen “credible reports” that support the filtration camp claims.

“I do not need to spell out what these so-called filtration camps are reminiscent of. It’s chilling, and we cannot look away,” she said in an address to the UN Security Council, alluding to Nazi-era concentration camps. “Every day we see more and more how little Russia respects human rights.”

“The world has not seen the scale of the tragedy in Mariupol since the existence of the Nazi concentration camps. Russia-occupation forces turned our entire city into a death camp,” Boychenko said this week. “This is the new Auschwitz and Majdanek.”

The mayor said that an estimated 5,000 Mariupol residents have been killed. The Russian troops have been using a mobile crematorium in a bid to hide the bodies.

The horrific crime in the Bucha town, where bodies of hundreds of locals were found with gunshot wounds scattered on the streets, triggered an outcry from the world. The “war crime” forced the United Nations Human Rights Council removing Russia.