It came as Boris Johnson spoke on Sunday night with Volodymyr Zelensky, the Ukrainian president, to ask for “an assessment of Ukraine’s military requirements” in advance of his meetings with G7 and Nato leaders this week.

Ten million people — around a quarter of the population — have now fled their homes in Ukraine due to Russia’s “devastating” war, the United Nations refugees chief said on Sunday.

Vadym Boichenko, Mariupol’s mayor, likened the deportations to “the horrific events of World War II, when the Nazis forcibly captured people”.

He said: “It is hard to imagine that in the 21st century, people can be forcibly taken to another country.”

On March 7, Kyiv rejected an offer from Moscow to create “humanitarian corridors” from heavily bombed Ukrainian cities after it emerged that most of the supposedly safe routes led directly to Russia or its ally, Belarus. The move prompted Emmanuel Macron, French president, to accuse Putin of “moral and political cynicism”, adding “I do not know many Ukrainians who want to go to Russia.”

Lyudmyla Denisova, Ukraine’s human rights commissioner, told Ukrainian TV the evacuees to Russia were taken to “filtration camps where the occupying forces were checking people’s phones and documents”.

She said they were taken to Taganrog, the closest Russian city over the border from Mariupol, and some were then sent by rail to “economically depressive Russian cities”.

“Our citizens were given documents that oblige them to stay in a particular town, meaning they have no right to leave it for at least two years and they have to seek employment there,” she said on Ukraine’s Channel 24.

America’s ambassador to the United Nations said reports of the deportations were “horrific” and “unconscionable” if true.
Linda Thomas-Greenfield said: “Certainly, that would be another escalation, but not beyond the realm of possibility given how the Russians have tried to put pressure on the Ukrainian people.”

Hundreds of thousands remain trapped in the Black Sea port of Mariupol, which has been under siege for three weeks and where conditions are dire. Russian and Ukrainian forces on Sunday continued to fight for control, with Moscow’s troops having advanced in recent days into the city centre.

Read the latest news on the Russia Ukraine conflict in today’s live blog