KINSHASA, Congo – The systematic rape of 303 men, women and children in eastern Democratic Republic of Congo was “cold-blooded,” the United Nation’s human rights chief said Friday.

“The scale and viciousness of these mass rapes defies belief,” said U.N. High Commissioner for Human Rights Navi Pillay, as initial results of a probe into the unprecedented assault were released.

“Even in the eastern part of DR Congo, where rape has been a perennial and massive problem for the past 15 years, this incident stands out because of the extraordinarily cold-blooded and systematic way in which it appears to have been planned and executed.”

According to the report, 235 women, 52 girls, 13 men and 3 boys were raped, some several times, over the course of four days in the Walikale region between July 30 and Aug. 2.

Around 200 heavily armed members of three militia groups, including the Hutu rebel group Democratic Forces for the Liberation of Rwanda, cut off the villages before embarking on the raping spree.

According to the report, one group would rape and loot in a village while others were setting ambushes to catch those fleeing through the forest. These people would then be raped or taken for forced labor.

The final number of victims may be higher because attacks were ongoing in some villages and many people were still hiding in the forest for fear of further attacks, the report said.

The report, prepared by a team that visited 13 affected villages, said serious shortcomings in the Congolese army and local police stopped them from acting, and also pointed the finger at the U.N. peacekeeping mission, known as MONUSCO.

“It (the report) also notes that their failure to prevent or stop the attacks was compounded by subsequent failings on the part of MONUSCO forces, which … suffered from a number of operational constraints,” Pillay’s Office of the High Commissioner for Human Rights said in a statement.

MONUSCO, which has a base close to the attack sites, has since stepped up patrols in the area.

Sexual violence has become a huge problem in Congo, which is still recovering from a full-scale conflict that ran from 1998 to 2003. An estimated 5.4 million people have died as a result of the conflict and its aftermath.

Rebel and militia groups continue to roam the east of the country — raping, looting and raking in cash by illegally mining minerals for use in consumer electronics.

The report said the militia used mass rape as a tool to subjugate local populations believed to be pro-government.

“So long as this free-for-all continues, with the mines and quarries controlled by armed groups or other rogue elements, the local population will be prey to attacks such as these,” she said.