South Sudanese President Salva Kiir disbanded his Cabinet last week. His country has struggled to maintain a sense of security two years after gaining independence from Sudan.
U.S. Secretary of State John Kerry spoke by phone with Kiir to express his concern about the political situation in South Sudan.
"I was present for South Sudan's historic, peaceful referendum, and I saw firsthand the hopes of a people for a better future," he said in a statement Saturday. "Too much sacrifice has been made to see that effort go backwards."
Washington helped broker the peace agreement with Sudan in 2005, which paved the way for a South Sudanese referendum for independence in 2011.
Kerry estimated there were 100,000 people affected by ongoing fighting in South Sudan.
Former South Sudanese Vice President Riek Machar said Kiir was operating within his presidential powers to disband the government.
"There should be no violence," he was quoted by the independent Sudan Tribune as saying.
Spokesman Barnaba Marial Benjamin confirmed Kiir's announcement Wednesday, saying a Cabinet makeover was long overdue.