The US said on Wednesday it has evidence that “hundreds of thousands” of Ukrainian citizens have been interrogated, detained and forcibly deported to Russia in “a series of horrors” overseen by officials from Russia’s presidency.

Russia immediately dismissed the allegation as “fantasy”, calling it the latest invention in a Western disinformation campaign.

The charge came during a Security Council meeting called by the US and Albania to discuss Russia’s “filtration operations”.

That involves Ukrainians voluntarily fleeing the war in their homeland and those forcibly being moved to Russia passing through a series of “filtration points” where treatment allegedly ranges from interrogations, data collection and strip searches to being yanked aside, tortured, sent to a detention centre in Russia and never seen again.

US ambassador Linda Thomas-Greenfield said estimates from a variety of sources, including the Russian government, indicate that Russian authorities have interrogated, detained and forcibly deported between 900,000 and 1.6 million Ukrainians.

She said they are sent to Russia, often to isolated regions in its far-eastern regions.

“These operations aim to identify individuals Russia deems insufficiently compliant or compatible to its control,” Ms Thomas-Greenfield said.

“And there is mounting and credible evidence that those considered threatening to Russian control because of perceived pro-Ukrainian leanings are `disappeared’ or further detained.”

Russia’s presidency is not only coordinating filtration operations but is providing lists of Ukrainians to be targeted for filtration, she added.

She said estimates indicate thousands of children have been subject to filtration, “some separated from their families and taken from orphanages before being put up for adoption in Russia”. According to US information, “more than 1,800 children were transferred from Russian-controlled areas of Ukraine to Russia” just in July, she said.

Russia’s UN ambassador, Vassily Nebenzia, accused the West of trying to besmirch his country.

He said more than 3.7 million Ukrainians, including 600,000 children, have gone to Russia or Russian-controlled separatist areas in eastern Ukraine, but they “aren’t being kept in prisons”.

“They are living freely and voluntarily in Russia, and nobody is preventing them from moving or preventing them leaving the country,” he said.

Mr Nebenzia said those Ukrainians went through “a registration rather than filtration procedure” similar to that for Ukrainian refugees in Poland and other countries in the European Union.

He said that since “we’ve wasted time talking about the latest conjectures and fantasies” on Wednesday, Russia is proposing that the Security Council hold a meeting on Thursday “on real threats to international peace and security caused by the supply by foreign states of arms and military goods to Ukraine”.

French ambassador Nicolas De Riviere, the current council president, scheduled the meeting for Thursday afternoon.

It will be the third consecutive Security Council meeting on Ukraine. On Tuesday, the council held a meeting at Russia’s request to hear about the situation at the Zaporizhzhia nuclear plant in south-eastern Ukraine.

Ukraine and Russia have accused each other of shelling the facility and threatening a possible nuclear catastrophe.

Ms Thomas-Greenfield said the US knew Russia would deny using filtration, “but there’s a simple way to know if any of this is true”.

“Let the United Nations in,” she told Mr Nebenzia and other council members. “Give the independent observers access. Give NGOs access. Allow humanitarian access. Let the world see what is going on.”