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 United Nations says the conflict has produced a million refugees.