The Prosecutor General's Office said this in a post on Facebook, Ukrinform reports.
During their meeting, Kostin and Harris discussed joint efforts to build a network of comprehensive accountability for international crimes and considered strengthening bilateral cooperation in the field of international legal assistance.
"We are sure that only by breaking the cycle of impunity can we pave the way to restore peace and prevent international crimes from being committed in the future. I sincerely hope our fruitful partnership will continue," Kostin said.
Kostin also thanked Harris for the United Kingdom's unwavering support for Ukraine and expressed his gratitude to Attorney General for England and Wales Victoria Prentis for her determination on the way to restore justice.
Earlier reports said that 45 OSCE member states had declared the need to punish Russia for war crimes it committed in Ukraine.