"I call upon the authorities of both countries to investigate these allegations," Margot Wallstroem, the UN secretary-general's special representative for sexual violence in conflict.
The UN's Office for the Coordiation of Humanitarian Affairs (Ocha) is investigating the rapes and sexual violence, according to Maurizio Giuliano, Ocha's spokesperson in Kinshasa, but "Angola and the DRC have to say who the perpetrators are."
Allegations of mass rapes stem from two separate areas. In southwestern Kasai province, there are reports that 657 people were sexually violated, but Ocha has not been able to verify this yet, says Giuliano.
"That's why a mission is going next week to figure out whether the 657 can be verified and how many of the cases of sexual violence are rapes, and if [the victims] were men or women," says Giuliano.
Sexual violence has also been reported from Angola to Bas-Congo province and Bandundu province.
Mass rapes took place earlier this year in the Kivus, in the eastern part of the Congo, thousands of miles away from this recent report.
"It's shocking that is a conflict context and a non-conflict context we have a situation of widespread sexual violence," says Giuliano.
"There are some indications that in at least some parts of the country, rape is indeed becoming endemic," he says.