JUBA, South Sudan — Brutal sexual violence committed with ‘‘pervasive impunity’’ and a level of ‘‘premeditation’’ persists in South Sudan’s northern region, the United Nations said on Friday.

At least 134 women and girls were raped, including some as young as 8, between September and December last year, according to a report issued by the UN Human Rights Office and the UN Mission in South Sudan. An additional 41 women suffered different forms of sexual and physical violence, said the report.

Even though South Sudan signed a fragile peace deal on Sept. 12 to end the country’s five-year civil war, which killed almost 400,000 people, the UN warns that endemic conflict-related sexual violence continues in northern Unity state. The UN investigation comes soon after outrage that followed a report by Doctors Without Borders which said that 125 women and girls had been raped, whipped, and clubbed in a 10-day period in the region at the end of November.

Almost 90 percent of the women and girls were raped by more than one perpetrator and often over several hours, said the UN report. Pregnant women and nursing mothers were also among the victims, including one mother who was nine months pregnant.

Most of the attacks were carried out by youth militia groups loyal to First Vice President Taban Deng Gai as well as South Sudan’s government army, said the report.

Internal documents seen by the Associated Press detailing the locations, scale, and dates of the attacks, showed they occurred in areas under control of forces allied to the First Vice President, according to a South Sudan security expert who spoke on condition of anonymity because wasn’t authorized to speak to the press.

Associated Press

The government is conducting its own investigation into the charges, however after a preliminary inquiry it denied that the accounts were real.