Ukrainians are being arbitrarily detained and subjected to enforced disappearances in Russian-controlled areas, the UN has told the BBC.
At least 36 cases of civilian detentions were verified by the UN, with families often denied any information about the fate of those being held.
Ukrainians say they fear an escalating campaign of kidnappings and intimidation, as Russia struggles to assert control over towns it captures.
Viktoriia Roshchyna, a journalist, was working in occupied areas in the east of the country when she was taken by unidentified men on 15 March.
Her employer, Hromadske media, said she "was probably detained by the FSB", Russia's internal intelligence service, based on witness accounts of her being taken in the city of Berdyansk.
She was released six days later when a hostage-style video - apparently recorded under duress - began to circulate on pro-Russian Telegram outlets. In it Roshchyna said Russia had not taken her captive and thanked Moscow's forces for "saving her life".
An elderly father held hostage
Svetlana Zalizetskaya, a journalist in the occupied city of Melitopol, accused Russian forces of taking her 75-year old father hostage as punishment for her refusal to co-operate with the new administration.
Zalizetskaya, the director of local news agency RIA Melitopol, wrote on Facebook that her father had been detained after her meeting with the Russian-installed leader of the city, where she refused to end her criticism of the invasion.
She said that she received a phone call from his captors, in which her father informed her that he was being held "in some basement" and said that he "didn't know what they wanted from him".
His captors demanded that Zalizetskaya, who has pledged to "tell the world of atrocities" committed by Moscow's forces in Melitopol, surrender herself.
Ukraine's National Union of Journalists (NUJ) said four journalists had also been detained and were later released in Melitopol.
The head of the Ukrainian NUJ, Sergiy Tomilenko, said the detentions were part of "a wave of information cleansing" which is aimed towards the "intimidation of journalists and public figures".
