The United States, European Union, Britain and a group of East African countries say South Sudan's government and rebel forces should immediately adhere to a permanent cease-fire.
The statement issued by the State Department is the first such call for a permanent cease-fire since deadly fighting erupted in South Sudan's capital in July. Civil war broke out in the country in late 2013 and violence has never stopped, despite a year-old peace deal.
The new statement calls the continuing conflict "senseless."
Hundreds have died in fighting around the country since July, according to both the government and rebels. Rebel leader Riek Machar, who fled the country and is now in neighboring Sudan, recently called for armed resistance.
Government spokesman Michael Makuei denies there is any fighting in his country.