NAIROBI (Reuters) - South Sudanese soldiers brutally raped an elderly woman and a pregnant woman lost her baby after being gang-raped by seven soldiers, according to United Nations investigators.

The U.N. human rights investigators presented the testimonies on Friday, saying increasingly brutal attacks on women are an integral part of spreading ethnic cleansing. They said the violence could spill into genocide.

“The scale of gang rape of civilian women as well as the horrendous nature of the rapes by armed men belonging to all groups is utterly repugnant,” said the chairwoman of the U.N. independent commission on human rights, Yasmin Sooka.

“Women are bearing the brunt of this war along with their children ... rape is one of the tools being used for ethnic cleansing.”

South Sudan became independent from Sudan in 2011 and had a brief period of celebration before ethnic tensions erupted amid allegations of widespread corruption.

In December 2013, fighting broke out months after President Salva Kiir, from the Dinka ethnic group, sacked vice president Riek Machar, a Nuer.

The sporadic fighting has increasingly taken on ethnic dimensions. Many of the smaller tribes accuse the Dinka of targeting them. Rebels have also targeted Dinka.

Women across the country were being subjected to sexual slavery, tied to trees and gang-raped or passed from house to house by soldiers, said Sooka, who said rebels were also committing atrocities.

Three in five women in U.N.-administered “protection of civilian” sites around the capital Juba experienced rape or sexual assault, according to a 2016 report by the U.N. Population Fund. The sites are meant to offer safe shelter for civilians.

Government officials and commanders on all sides had a legal duty to prevent their soldiers from preying on civilians, said Sooka’s colleague Kenneth Scott, a former prosecutor.

“Commanders, officers will be held accountable for failing to exercise command and control,” he said, warning failure to prevent atrocities could result in prosecution.

The shaky 2015 peace agreement that was supposed to end the latest round of fighting provided for a hybrid court to be set up with responsibilities divided between the African Union and South Sudan, but progress on setting it up was “very slow”, Scott said.

South Sudanese officials were not available to comment on the investigators’ findings, but on Thursday, Kiir told Reuters that no ethnic cleansing was taking place in South Sudan. The military has repeatedly denied targeting civilians.

Scott said the government had had almost “no reaction” to the commission’s findings.