A new report by a U.S.-based watchdog group accuses South Sudan's rival leaders of amassing wealth abroad amid a conflict in which tens of thousands have been killed.

The report by The Sentry says President Salva Kiir, former deputy Riek Machar and those close to both men have looted the country in accumulating wealth that includes mansions and luxury cars abroad.

The report says it has obtained images of their family members partying in five-star hotels as well as documentation of their offshore properties.

South Sudan 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.