Crew members of the Ukrainian naval vessels captured and still held by Russians in Moscow could be considered as prisoners of war and protected under the Geneva Convention. This is stated in the report of the Office of the United Nations High Commissioner for Human Rights on the human rights situation in Ukraine for the period from Nov. 16, 2018 to Feb. 15, 2019.
Russia's War Against Ukraine
Ukrinform: UN says Ukrainian sailors captured by Russia are prisoners of war
Captured Ukrainian sailors Yury Budzilo, Sergey Chuliba, Yury Bezyazychny and Bogdan Nebylitsa in the courtroom, in Moscow, Feb. 13, 2019.