The young mother of two was walking with her sister near a desolate highway in northern Ethiopia last month when five men forced them into a pickup truck and drove them to a small building with a metal roof.

The women recognized their captors by their accents and military uniforms: They were soldiers from neighboring Eritrea, which has joined Ethiopian troops in months of fighting against anti-government forces in the Tigray border region.

Mehrawit, 27, was separated from her sister and locked in a room with only a thin, dirty mattress. For two weeks, she said, the Eritrean soldiers gang-raped her repeatedly, fracturing her spine and pelvis and leaving her crumpled on the floor. One day, she counted 15 soldiers who took turns sexually assaulting her over eight hours, her cries of agony punctuated by their laughter.