GENEVA — Some women were tied to trees, raped for hours and then beaten. Others who resisted were pummeled with rifle butts, sticks and cable wire. The assailants were armed men, mostly from forces aligned with South Sudan’s government.

Nearly five months after South Sudan’s warring leaders signed an agreement to end five years of conflict in the country, which was only founded in 2011, the United Nations on Friday listed those horrific practices to voice alarm about an upsurge in sexual violence there that started late last year.

United Nations investigators said they had documented the rape of 134 women and girls in northern areas of South Sudan in the last three months of 2018. Fifty of the victims were children, one of them just 8 years old. Another 41 women and girls suffered other forms of sexual and physical abuse.

Many rape victims had dispersed to remote areas that could not be reached by road, and the actual number of attacks was much higher, the investigators said, noting that the violence had continued this year, albeit on a smaller scale.