NAIROBI, Kenya  More than 600 women and girls were recently raped along the Congo-Angola border during a mass expulsion of illegal immigrants, according to the United Nations.

Many of the victims said they were locked in dungeon-like conditions for several weeks while they were raped repeatedly by security forces. At least one woman died from her internal injuries, United Nations officials said.

Maurizio Giuliano, a United Nations spokesman in the Democratic Republic of Congo, said Friday that it was unclear on which side of the Congo-Angola border the women had been attacked, and that the United Nations was calling on both countries to investigate promptly.

“What worries us is that rape seems to be becoming endemic in several parts of Congo,” Mr. Giuliano said, also referring to recent rapes in the eastern Kivu provinces. “We fear it’s becoming part of the routine.”