However, the patterns suggest that sexual violence “maybe even more frequent” in territories that were occupied for longer periods, he added, without providing evidence.
Widespread or systematic sexual violence could amount to crimes against humanity, which are generally seen as more serious, legal specialists said.
Moscow, which has said it is conducting a “special military operation" in Ukraine, has denied committing war crimes or targeting civilians.
Evidence that sexual violence was planned could indicate it was part of a systematic attack or that some level of command was aware, said Kim Thuy Seelinger, an advisor to the ICC on sexual violence in conflict and a research associate professor at Washington University in St. Louis.
Ukraine’s Prosecutor General’s office said it has opened dozens of criminal cases involving sexual violence by members of the Russian armed forces against women, children and men.