The State Department issued a travel warning for South Sudan, saying it advised against traveling to areas that border Sudan. Though fighting between rival forces has declined since early this year, renewed conflict remains a legitimate threat.
"If you are currently working on humanitarian relief or development efforts in Juba, or anywhere in South Sudan, you should take measures to reduce your exposure to violent crime, and should closely follow the security policies and procedures of your organization," the warning read.
A driver employed by the U.N. World Food Program was killed in early August while working in the restive Sudanese state of South Kordofan.
Early this week, a similar warning was issued by the State Department for Sudan, describing the threat level from terrorist attacks on Darfur as critical.
South Sudan gained independence last year as part of a peace deal with Sudan. Ethnic fighting, border conflicts and disputes over oil have threatened the deal, however.