Last week, the ministry of health reported that an unknown disease had killed dozens of people in the area which is one of the worst hit by recent flooding.

A local health official said initial samples collected in the area returned negative test results for cholera.

"We decided to send a rapid response team to go and do risk assessment and investigation; that is when they will be able to collect samples from the sick people – but provisionally the figure that we got was that there were 89 deaths,” WHO’s Sheila Baya told the BBC.

She said Fangak area was not reachable by land due to flooding and the team was waiting for a helicopter to return them to the capital, Juba, on Wednesday.