Russia is violating the "fundamental principles of child protection" in wartime by giving Ukrainian children Russian passports and putting them up for adoption, the U.N.'s refugee agency (UNHCR) chief told Reuters in an interview.

Speaking at the UNHCR offices in Kyiv following a six-day tour of the country, Filippo Grandi said Ukraine's president had asked his agency to "do more" to help children from occupied regions to whom this was happening.

"Giving them (Russian) nationality or having them adopted goes against the fundamental principles of child protection in situations of war," Grandi said.

"This is something that is happening in Russia and must not happen," he added.

President Volodymyr Zelenskiy, speaking after his meeting with Grandi on Wednesday, called for mechanisms to be set up to "defend and return" children and adults deported to Russia, as well as to punish those responsible.

Grandi said his agency was unable to estimate the number of children who had been given passports or put up for adoption, as access in Russia was extremely limited.

"We are seeking access all the time, and access has been rather rare, sporadic and not unfettered, if you see what I mean."

Russia has said accusations Ukrainian children have been abducted are false.

"We categorically reject unfounded allegations that the Russian authorities are kidnapping children," Russian diplomat at the United Nations Dmitry Polyansky said in July, according to the TASS news agency.

FUTURE TRENDS

Grandi highlighted two potential future trends in Ukraine's displacement crisis, which saw eight million Ukrainians flee abroad and several million more become internally displaced after Moscow's Feb. 24 invasion last year.

The UNHCR chief said more refugees could return to Ukraine in the warm season, as happened in 2022 when the agency observed "hundreds of thousands" of returnees at the end of the summer- although that movement was halted by the onset of the cold.

Ukraine's typically icy winter has been made harsher still this year by Russia's campaign of missile strikes against its neighbour's energy infrastructure, leading to outages of power, water and heat supplies in major cities.

“We have seen returns drop considerably, long or short, in the winter months… coupled with a very slight increase with people getting out of the country,” he said.

Grandi also warned that an escalation in fighting could trigger a new wave of refugees, although these are likely to mostly be internal.

“What we have seen in the last few days is not very promising in this respect, everybody foresees that there will be a rise in hostilities, an escalation… and this is likely to generate a more displacement.”

GLOBAL VIEW

Grandi painted a bleak global outlook, predicting that the number of displaced people, currently at 103 million, would "almost inevitably" grow in the coming years if the UN Security Council continued to be divided on key issues.

"If the world's supreme body to maintain peace and security is not able to do its job because of international divisions, then conflicts will continue to... expand, continue, not be resolved."

"That's what causes the 103 million to almost inevitably grow."

The UNHCR chief also urged countries to process prospective asylum seekers more quickly in order to stop unfounded asylum claims from clogging up the system.

"Don't drag it out! Because dragging it out means that people abscond, they disappear, they become illegal immigrants, and then its a big problem because nobody knows how to send them back," he said.

"Governments have to take more decisive action in doing that." (Additional reporting by Emma Farge in Geneva and Caleb Davis; Editing by Frank Jack Daniel)