South Sudan's government says it will take legal action against a US-based watchdog that has accused the leaders of the country's warring sides of amassing fortunes during a nearly three-year conflict that has left tens of thousands dead.

The Sentry group, founded by US actor George Clooney and rights activist John Prendergast, alleged on Monday that President Salva Kiir, opposition leader Riek Machar, and those close to them had looted state coffers, accumulated luxury homes and cars, and enriched themselves and family members through stakes in oil and other business ventures.

South Sudan leaders 'profit' as country suffers during war

Responding to the allegations, presidential spokesman Ateny Wek Ateny said on Tuesday that even though there was corruption in the country, the statements that had been made against Kiir and other government officials were "completely rubbish".

"Their statement is a mere recipe for fueling gross misconception about the leadership of South Sudan," Ateny told Al Jazeera, accusing Clooney and Prendergast of conducting a "politically biased" investigation.

"We will [take] them to court; we will hire the law firm in the US and we will sue them because they have relied on evidence that is completely rubbish," he said from the capital Juba.

"They were actually interviewing 100 people who ... only came to give evidence on condition of anonymity ... but at the end of the day, [their identity] will be disclosed, because if we go to the court of law they will have to be disclosed."

OPINION: South Sudan, a country captured by armed factions

James Gatdet Dak, a spokesman for Machar, also denied that the rebel leader owned property in either Kenya or Ethiopia, as the report alleged.

"It is a lie. Dr Riek Machar's family does not own a house in Nairobi or in Addis Ababa as alleged," he told Reuters news agency.

"They are renting a house in Nairobi, while the one in Addis Ababa was a temporary guesthouse provided to him by the Ethiopian authorities during the peace negotiations."

'Violent kleptocracy'

The two-year inquiry charged that Kiir and Machar, and their cronies, had amassed fortunes, including foreign properties and stakes in international firms, while prosecuting a ruinous conflict that has forced 2.5 million people from their homes.

Salva Kiir and Riek Machar: South Sudan's shaky peace - Talk to Al Jazeera

Top officials' families "often live in multimillion-dollar mansions outside the country, stay in five-star hotels, reap the benefits of what appears to be a system of nepotism and shady corporate deals, and drive around in luxury cars," the report said.

The report also accused a system of international banks, businesses, arms brokers, real estate firms and lawyers of "knowingly or unknowingly facilitating the violent kleptocracy that South Sudan has become".

"There's a lot of people here who have accumulated a great deal of wealth," said Al Jazeera's Anna Cavell, reporting from Juba.

"This report raised the idea of someone looking into their bank accounts or checking on the registration of their companies, and that’s made a lot of people very uneasy."

South Sudan, the world's youngest nation, plunged into conflict soon after Kiir fired Machar from his post as vice president in 2013.

A peace deal reached a year ago under international pressure has been violated repeatedly by fighting, and Machar fled the country in recent weeks.

Source: Al Jazeera News And Agencies