Secretary of State John Kerry is severely criticizing South Sudan's warring president and opposition leader, and pledging U.S. funds to create a court to hold them accountable for crimes.

Speaking in Kenya, Kerry says President Salva Kiir and former Vice President Riek Machar are squandering the promise of the world's youngest country. He says they must compromise in the interests of peace.

Tens of thousands have been killed in a power struggle that has raged since December 2013. More than 2 million are uprooted from their homes.

In an emotional appeal, Kerry on Monday demanded that Kiir and Machar "silence the guns."

And in an implicit threat, he said the U.S. would provide $5 million in new money to help create a court "to hold perpetrators of violence to account."