While they stoked war and famine throughout their stillborn country, South Sudan's top brass amassed fortunes with the help of international banks, businesses and brokers, according to a new investigation.

Key beneficiaries named by the Sentry, an international advocacy group, include President Salva Kiir and former vice president Riek Machar, the two men whose deadly feud prompted South Sudan’s descent into war three years ago.

Tens of thousands of people have died in the conflict since 2013, dividing much of the country along ethnic lines, with Kiir’s predominantly Dinka troops fighting Machar’s Nuer followers. South Sudan gained independence from its northern neighbor in 2011 after years of international mediation led by the United States.

“President Kiir and Vice President Machar have traded accusations about corruption and abuse of power. But make no mistake, the current war is not about changing the system in South Sudan; it is about who controls it,” said the Sentry in a report released Monday. The organization was set up by Hollywood actor George Clooney and the American human rights activist and former Clinton administration official John Prendergast.

At a news conference in Washington on Monday, Clooney linked the corruption found in the investigation to its purveyors' propensity toward violence. "They are stealing the money to fund their militias to attack and kill one another," he said. "Whoever is in power in government has the purse strings and is then able to purchase weapons and use those. That is why money is important."

Although Kiir’s official salary stands at just $60,000, the Sentry’s investigators tracked his wealth to luxury mansions in South Sudan and Kenya. It also found that family members — including Kiir's 12-year-old son — owned major stakes in businesses across the country’s major industries, including oil, mining, construction, aviation and military procurement. South Sudanese law bars officeholders from engaging in commercial activity.

Likewise, investigators traveled to newly built homes owned by the Machars in the Kenyan and Ethiopian capitals. The report contains pictures of a relative of Machar standing in front of a large house in a gated community outside Nairobi, in a driveway with four high-end SUVs. Machar recently fled South Sudan after an outbreak of violence followed failed peace talks, and he is reportedly undergoing medical procedures in Khartoum, Sudan's capital.

Although the United Nations has imposed financial sanctions against six South Sudanese military commanders, the report found that at least two of the men were still able to move their money outside the country with relative ease, apparently with the help of  a Ugandan middleman.

"I’ve never seen anything so brazen in my time as an investigator," said J.R. Mailey, a senior policy analyst at the Sentry who worked on the report. He said his approach to a relative of one top government official had even resulted in an invitation to sign on to a mining deal that allegedly involved the president.

The report recommends freezing the assets of Kiir, Machar and numerous generals.

During a U.S. House of Representatives hearing last week, several U.S. lawmakers called for additional international sanctions to be imposed on individuals blamed for the ongoing violence. The United States is by far and away the largest contributor of foreign aid to the South Sudanese government.

"There must be consequences for those who are found guilty," said Rep. Christopher H. Smith (R-N.J.), the chairman of the subcommittee that held the hearing, referencing allegations of war crimes against troops controlled by Kiir and Machar.

Donald Booth, the U.S. special envoy to South Sudan, assured the panel of representatives that their concern would be relayed, but he was met with stinging skepticism.

"If we make too many idle threats and don't follow through on them, eventually they become irrelevant," said Rep. Mark Meadows (R-N.C.).

Almost 1 in 6 South Sudanese residents have been forced to flee their homes, and more than 5 million are urgently in need of humanitarian assistance, according to the United Nations. Violence in Juba has subsided since clashes broke out there in July — but the rainy season, which generally impedes troop movement, is nearing its end.

Read More: