South Sudan's political and military elite have made themselves rich while the country has struggled under a civil war of their making, a report says.
Commissioned by actor George Clooney, the document accuses President Salva Kiir, opposition leader Riek Machar, and top generals of profiteering.
It follows the trail of money with links to the families of both Mr Kiir and Mr Machar.
Those named have not yet responded to the allegations.
The BBC is seeking comment from them.
The report's authors spent two years collecting evidence and testimony on behalf of a new investigative unit - called The Sentry - which was co-founded by the US actor.
Mr Clooney said the evidence was "detailed" and "irrefutable" and that it was time for the world to take action.
The actor said international lawyers, banks and real estate were involved in criminal behaviour linked to the militias and innocent civilians were paying the price.
"They're stealing the money to fund their militias to attack and kill one another," he said.
"We can either take action or we can spend the next decade mopping up the mess."
'Rival factions of kleptocratic network'
Entitled War Crimes Shouldn't Pay, the report has found that "top officials ultimately responsible for mass atrocities in South Sudan have at the same time managed to accumulate fortunes, despite modest government salaries".
"Some have been involved in questionable business deals while others have apparently received large payments from corporations doing business in South Sudan."
A man walks past a destroyed tanks in Juba. Photo: July 2016
The civil war that erupted in 2013 has devastated the country
A fall-out between President Kiir and former Vice-President Machar - the most powerful members of their respective Dinka and Nuer ethnic groups - led to the civil war which erupted in December 2013.
Terrible atrocities have been carried out by both sides - often along ethnic lines.
Mass rape has been used as a weapon of war and United Nations reports have detailed human rights abuses.
Some 2.5 million people have been forced from their homes, and millions more need food aid.