U.S. Secretary of State Antony Blinken has accused Russia of forcibly deporting hundreds of thousands of Ukrainians from areas it controls in the east and south of the country to Russia.

Blinken said an estimated 900,000 to 1.6 million Ukrainian citizens, including 260,000 children, have been interrogated, detained, and deported from their homes to Russia, including to isolated areas in the Far East, through filtration operations.

In a statement on July 13, Blinken called on Russia to stop these operations, which he said violate the Geneva Conventions.

“The unlawful transfer and deportation of protected persons is a grave breach of the Fourth Geneva Convention on the protection of civilians and is a war crime,” Blinken said.

The filtration operations are separating families, confiscating Ukrainian passports, and issuing Russian passports “in an apparent effort to change the demographic makeup of parts of Ukraine,” Blinken said in the statement.

The people who are “filtered out” include Ukrainians deemed threatening because of their potential affiliation with the Ukrainian military, media, government, and civil society groups, Blinken said.

He also cited eyewitness reports from survivors who said that Russian authorities had transported tens of thousands of people to detention facilities in Donetsk controlled by Moscow-backed separatists, where many are reportedly tortured.

There are reports that some individuals targeted for filtration have been summarily executed, he said.

The filtration program appears to have been planned early and matches similar operations that Russia undertook in other wars, including in Chechnya, he said, adding that the Russians must be held accountable.

“This is why we are supporting Ukrainian and international authorities’ efforts to collect, document, and preserve evidence of atrocities,” he said.

The statement came a day before the Ukraine Accountability Conference in The Hague on alleged war crimes in Ukraine.

Some information for this report was provided by Agence France-Presse.