A UN rights commission in South Sudan said Friday there was sufficient evidence to charge at least 41 senior officers and officials with war crimes and crimes against humanity.
South Sudan's four-year-old civil war has been characterised by extreme brutality and attacks on civilians.
But no high-ranking officials have been held to account, despite African Union (AU) promises to establish a special court to try alleged crimes.
"The court could be set up straight away and the prosecutor could begin working on indictments," said Yasmin Sooka, chairperson of the UN Commission on Human Rights in South Sudan.
"Under the peace agreement, those indicted can no longer hold or stand for office. Ultimately this is the only way to stop the rampant devastation of millions of human lives by South Sudan's leaders," she said.
The commission said it had forwarded a confidential list of suspects to the UN's High Commissioner for Human Rights, Zeid Ra'ad Al Hussein. Those named comprise three state governors, 33 generals and five colonels.
The report -- based on 58,000 documents and 230 witness statements -- is a litany of horrors and extraordinary cruelty. Some victims were beheaded, burned alive or had their throats cut, others had their eyes gouged out or were tortured.
Rape 'reminiscent of Bosnia'
Sexual violence was particularly prevalent with numerous accounts of gang rape and child rape, and in "cases reminiscent of Bosnia" of people forced to watch or participate in the rape of loved ones.
In one instance a 12-year-old boy was forced to have sex with his grandmother or be killed.
Men were also attacked, with some castrated and others raped.
"The Commission believes the prevalence of sexual violence against men in South Sudan is far more extensive than documented; what we see so far is likely just the tip of the iceberg," said Sooka.
The UN commission said soldiers and officials loyal to President Salva Kiir and rebel leader Riek Machar were both responsible for crimes.
It dismissed arguments that indisciplined soldiers might be to blame.
Both the government and rebel "military hierarchies functioned effectively in terms of issuance, transmission, and respect for orders," it said.
The commission said its investigations had focussed on incidents where it could make "the case for individual command responsibility for widespread or systematic attacks on civilians."
It found widespread looting and deliberate ethnic attacks on entire communities and villages, with the "destruction of dwellings... on an industrial scale."
The South Sudan war began as a battle between Kiir's majority Dinka tribe and Machar's Nuer.
But it has since metastasized, spreading and fragmenting, while feeding on local grievances and long-standing ethnic animosities over access to land, resources and power.
"There is a clear pattern of ethnic persecution for the most part by government forces who should be pursued for crimes against humanity," said Andrew Clapham, one of the commissioners.
Describing South Sudan's justice system as "dysfunctional" the commission called on the AU to establish the 'Hybrid Court', modelled on tribunals in Sierra Leone, Cambodia and elsewhere.
"There is sufficient evidence to conclude that... the parties to the conflict are deliberately targeting civilians on the basis of their ethnic identity and by means of killings, abductions, rape and sexual violence, as well as the destruction of villages and looting. These acts constitute war crimes and crimes against humanity," the commission's report said.
Disgust at the latest evidence of brutality was widespread.
Britain's foreign minister Boris Johnson said on Twitter, "Reports of atrocities in South Sudan are among most troubling I have seen. Sexual violence being used as weapon of war against women, men, children & elderly victims. UK supports peace efforts but S Sudanese must honour ceasefire for the sake of their people."
The last ceasefire, signed in December, was broken within hours while the latest round of peace talks in the Ethiopian capital Addis Ababa have stalled.
Seif Magango of rights group Amnesty International said the UN report demonstrated "the critical need to establish the Hybrid Court for South Sudan".
The report "should jolt the world into speedy action to address the horrific human rights violations that have continued unabated for four years of conflict in South Sudan," he said.