Trump administration officials want local health authorities to constantly monitor the 18 passengers for another three weeks, a requirement that far exceeds typical protocols.
The passengers who have been housed in the National Quarantine Unit at the University of Nebraska Medical Center were aboard a cruise ship that became the center of a global hantavirus outbreak this month.
The order came after U.S. officials said that a 50-bed facility was being established in the African country to house American citizens exposed to the virus.
But U.S. officials are still working to find centers in Europe to accept Americans who need advanced treatment, seen as critical to improving odds of survival.
The Ebola outbreak in the Democratic Republic of Congo is already estimated to have caused more than 1,000 cases and more than 200 deaths since it was announced May 15.