Sexual violence rampant in South Sudan's Unity area, says UN 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

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 eight, between September and December last year, according to a report issued by the U.N. Human Rights Office and the U.N. Mission in South Sudan. An additional 41 females suffered different forms of sexual and physical violence, said the report.

Even though South Sudan signed a fragile peace deal on September 12 to end the country's five-year civil war, which killed almost 400,000 people, the U.N. warns that endemic conflict-related sexual violence continues in northern Unity state. The U.N. investigation comes soon after outrage that followed a report by the medical charity Doctors Without Border which said that that 125 women and girls had been raped, whipped and clubbed in a 10-day period in the Unity 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 U.N. report. Pregnant women and nursing mothers were also among the victims, including one mother who was nine months pregnant.

"The volatility of the situation in South Sudan combined with the lack of accountability for violations and abuses committed throughout Unity, likely leads armed actors to believe that they can get away with rape and other horrific forms of sexual violence," said Michelle Bachelet, the U.N high commissioner for human rights.

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 that the areas where they occurred are 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.

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

"Nothing of this kind occurred in Bentiu," said Rabi Emanuel, the government representative at a meeting in Juba in January chaired by the Ceasefire and Transitional Security Arrangements Monitoring Mechanism, the group charged with overseeing the implementation of the peace deal.

The upsurge in sexual violence is partially attributed to large numbers of fighters on "standby," awaiting implementation of security arrangements under the new peace agreement, said the report.

By May, both government and opposition forces are expected to have been housed in barracks, trained and merged into one national army. However, with only three months left in the pre-transitional stage of the deal the security arrangements have not yet been implemented because of a lack of funds.