"The situation in South Sudan remains extremely volatile, with sporadic clashes between armed elements still taking place, forcing civilians to seek safety in U.N. facilities, religious establishments and other perceived havens," spokesman Rupert Colville said in a statement.
Conflict erupted last month when President Salva Kiir accused former Vice President Riek Machar of trying to topple his administration. Sidelined when Kiir reshuffled his Cabinet in July, the former vice president denies allegations of launching a coup.
Colville said approximately 60,000 civilians in South Sudan have been displaced by violence. Though the capital city Juba is relatively calm, the spokesman said authority over key cities elsewhere in the country has changed hands at least three times since fighting began.
The United States helped broker the peace deal that ended Sudan's civil war in 2005, paving the way to South Sudan's independence six years later.
Susan Rice, national security adviser for the White House, said both parties to the conflict have a responsibility to settle their differences peacefully.
"It is the obligation of both President Kiir and Mr. Machar to ensure that the lives of their people and future of their young country are not further marred by continued violence and atrocities," she said in a statement Thursday.