Desire Londroma Ndjukpa heads the Cooperative for the Development of the Congo (CODECO) militia, while Yakutumba, an army deserter, is leader of the armed Mai-Mai Yakutumba rebel group.
The U.K. Foreign Commonwealth and Development Office (FCDO) said Ndjukpa and Yakutumba would be subject to asset freezes and travel bans.
Both men's groups have used rape and mass rape, breaking international humanitarian law, the FCDO said.
"Threats of sexual violence as a weapon in conflict must stop and survivors must be supported to come forward," said junior foreign minister Tariq Ahmad.
"These sanctions send a clear signal to perpetrators that the UK will hold you accountable for your horrendous crimes."
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