The country claims more than 19,000 children have been illegally transferred to Russia or Russian-held territory.

Officials said the Russian and two Ukrainian suspects were the first to be charged in the matter.

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Prosecution documents seen by Reuters allege 48 children were forcibly displaced from a children's home in the formerly-occupied city of Kherson in September and October and taken to Moscow and occupied Crimea.

The children are said to have been aged between one and four. Prosecutors said their current location was uncertain.

Russia denies violating children's rights and says its forces were rescuing them from conflict zones.

The charges come after Sky News recently told the story of the daring escape of one group taken to Russia against their will.

"It was not a one-day event. Forty-eight children who were in the Kherson Region Children's Home were forcibly displaced, deported," said Yuliia Usenko, head of child protection in the prosecutor's office.

"We don't know how these children are, in what conditions they are kept, or what their fate is.

"They may have been illegally adopted by Russian citizens, or taken to Russian institutions," said Ms Usenko.

Most are alleged to have been taken on 21 October under the direction of the Russian suspect.

Prosecutors shared a video said to show one suspect helping put the children on a bus marked with the pro-Russian "Z" symbol.

The three suspects' names are redacted in documents - and they are thought to be in Russia or Crimea - but the trial could be held without them present.

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The charges, if proven, are against the Geneva Conventions and punishable by up to 12 years in prison under Ukrainian law.

The charges follow a wider investigation by the International Criminal Court.

In March, it issued arrest warrants for President Vladimir Putin and Russia's children's rights commissioner Maria Lvova-Belova over the claims.

The Kremlin called the move "outrageous and unacceptable" and said the warrants were "null and void".

Sky's international affairs editor, Dominic Waghorn, suggests the motivation for the alleged abductions is twofold: older children can be trained to serve in the military, while younger children are beneficial for Russian propaganda purposes.