GENEVA, Switzerland — Nearly 100,000 children live in institutions and boarding schools in Ukraine and parental consent should be sought before evacuating them abroad during the Russian invasion, the United Nations said Monday.

The heads of the UN agencies for refugees and for children made a joint plea for vulnerable youngsters caught up in the crisis to escape the conflict.

Unaccompanied and separated children fleeing the escalating conflict in Ukraine must be protected, UNICEF chief Catherine Russell and the UN High Commissioner for Refugees Filippo Grandi said.

But in the cases of those with living relatives or legal guardians, families should “under no circumstances” be separated as a result of relocation, they said.

More than 1.7 million people have fled Ukraine since the Russian invasion on February 24 — among them hundreds of thousands of children.

“Many are unaccompanied or have been separated from their parents or family members,” Russell and Grandi said, urging all destination countries to ensure their immediate identification and registration.

While temporary foster or community care offers critical protection, they said, “adoption should not occur during or immediately after emergencies”.

“Every effort should be made to reunify children with their families when possible, if such reunification is in their best interest.” Russell and Grandi said that nearly 100,000 children, half of them with disabilities, were living in institutional care and boarding schools in Ukraine — many of them having living relatives or legal guardians.

“We have received reports of institutions seeking to move children to safety in neighbouring countries or beyond,” they said.

Though humanitarian evacuations can be life-saving, it is critical that the consent of their parents or guardians be granted, the pair said.

“Under no circumstances should families be separated as a result of relocation or evacuation movements,” they stressed.

Meanwhile those legally responsible for children in institutions must ensure that evacuations are reported to the authorities in both Ukraine and the arrival country, and, as far as possible, with their identification papers and case files.