AWEIL, South Sudan -- South Sudan's government is challenging a new report by a U.S.-based watchdog group that says the country's leaders have amassed wealth abroad amid a conflict in which tens of thousands have been killed.

A spokesman for President Salva Kiir says the allegations by The Sentry report "can only jeopardize the pursuit of peace and stability in my country where mutual distrust and lack of authority are key factors of violence."

Ateny Wek Ateny's statement questions whether the report's sources really exist, and he says the allegations will be challenged.

The report by The Sentry, which was co-founded by actor George Clooney, charged that the civil war is being fueled by competition among rivals over national resources such as oil.

The report said Kiir, former deputy Riek Machar and those close to both men have looted the country in accumulating wealth that includes mansions, luxury cars and stakes in a number of businesses abroad. It included images of what it described as the properties abroad.

On Wednesday, a South Sudan newspaper, The Nation Mirror, said the government had ordered its shutdown the day it published a front-page story on the watchdog report.

South Sudan, which gained independence from Sudan in 2011, 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.

The United Nations on Friday announced that South Sudan conflict has produced a million refugees, a "very sad milestone" reached only by Syria, Afghanistan and Somalia.