Stephen Warikozi told The Associated Press that the captain of the Antonov AN-12 informed the control tower at Juba International Airport before taking off that he had 12 passengers and six crew members.
Only one person, an infant, survived the crash. There were believed to be even more people aboard the flight than those cited by the captain.
Warikozi said the plane's cargo capacity was 15.5 tons and that, according to the cargo manifest, the plane was carrying 15.5 tons of cargo.
Minister of Transportation Kuong Danhier Gatluak said the known death toll is now 37, up from 36. He said no more bodies were found at the site yet and attributed the change to a recount of the bodies and body parts at the hospital where they were brought.
The UN mission in South Sudan said it has provided a diving team to search the River Nile adjacent to the crash site and an engineering team to support efforts to cut open or remove debris.