The Red Cross said Monday it was trying to find out what happened to 23,000 people who have disappeared in the chaos of Russia's war in Ukraine.
The International Committee of the Red Cross said it was seeking to determine whether they had been captured, killed or had lost contact after fleeing their homes.
Shortly after Russia's full-scale invasion of Ukraine in February 2022, the ICRC created a special bureau of its Central Tracing Agency (CTA), dedicated to searching for those missing on both sides in the conflict.
"Not knowing what happened to a loved one is excruciating, and this is the tragic reality for tens of thousands of families, who live in a state of constant anguish," CTA bureau chief Dusan Vujasanin said in a statement.
"Families have the right to know what happened to their relatives and, when possible, to exchange news with them."
The ICRC said that over the past two years it had received more than 115,000 phone calls, online requests, letters and in-person visits from desperate family members from both Russia and Ukraine looking for missing relatives.
By the end of January, the organisation and its partners had helped provide 8,000 families with information, it said.
The statement quoted some of their reactions after receiving news about a loved one.
"I didn't hear anything for about two months. I felt dead during this time," it quoted one person as saying after hearing their son was alive.
Vujasanin stressed however that many other families "remain without news".
- Call for humane treatment -
The Geneva-based ICRC set up its CTA system more than 150 years ago.
But the Russia-Ukraine division is the first dedicated CTA bureau set up for a specific international armed conflict in more than 30 years and is its largest operation since World War II.
It acts as a neutral intermediary between Russia and Ukraine, collecting, centralising, safeguarding and transmitting information from one side to the other.
The ICRC stressed that families have a right under international law to know the fate and whereabouts of their missing relatives.
"People who are held by a party to the conflict must be treated humanely and the dead must be handled in a dignified manner," it said.
Yevheniia Filipenko, Ukraine's ambassador in Geneva, said Monday there were large numbers of civilians being held by the Russian authorities.
"Russia refuses to provide access -- to any humanitarian or human rights monitoring or investigative mechanisms, or humanitarian actors -- to these people," she told a briefing with the UN correspondents' association.
"We in Geneva receive, on a daily basis, calls from the relatives of those who are missing. And every call is a human life. We understand that, and we are trying to do our utmost to find out the whereabouts."
She encouraged all possible international actors to help determine the whereabouts of those missing.
"But the major obstacle is Russia's refusal to provide access, to provide information," she said.
"There is a need to put pressure on Russia as an occupying power, but also as a party to the Geneva Conventions, to comply with the provisions of the Geneva Convention and to provide information about the protected persons under the Geneva Convention."