South Sudan's government operated a "scorched earth policy" of deliberate rape, pillage and killing of civilians during the civil war in 2015, a report published on Friday by the United Nations human rights office said.
"The report contains harrowing accounts of civilians suspected of supporting the opposition, including children and the disabled, killed by being burned alive, suffocated in containers, shot, hanged from trees or cut to pieces," the UN human rights office said in a statement.
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The prevalence of rape "suggests its use in the conflict has become an acceptable practice by (government) SPLA soldiers and affiliated armed militias," the report said.
Groups allied to the government were allowed to rape women in lieu of wages, it said.
Between April and September 2015, the UN investigation recorded more than 1,300 reports of rapes in South Sudan's Unity State alone. In one incident soldiers argued over whether or not to rape a 6-year-old girl and ended up shooting her. Even women inside UN protected camps were at risk when they went out to collect food or firewood.
UN human rights chief Zeid Ra`ad Al Hussein said the number of rapes described in the report must only be a "snapshot of the real total", but the massive use as an instrument of war and terror had largely been off the international radar.
"The scale and types of sexual violence - primarily by Government SPLA forces and affiliated militia - are described in searing, devastating detail, as is the almost casual, yet calculated, attitude of those slaughtering civilians and destroying property and livelihoods," he said in a statement.
In one of many incidents, SPLA forces reportedly rounded up 60 cattle-keepers and locked them in a container in the compound of a Catholic church. All but one suffocated within two days.
In the 12 months to November 2015, there were an estimated 10,553 civilian deaths in Unity State, 7,165 of them due to violence and 829 caused by drowning. The patterns of killing were not random, isolated or accidental, but appeared to be deliberate, systematic and based on ethnicity, the report said.
Although all sides have committed atrocities that may amount to crimes against humanity, government forces were most responsible in 2015, the report said. There was little resistance in Unity State in 2015, leaving civilians at the mercy of government forces.
South Sudan's war began in December 2013, throwing the world's newest country into chaos, killing tens of thousands, displacing more than 2 million, and plunging at least 40,000 into a famine.