Cholera cases in war-torn Sudan increased by nearly 40% in less than two weeks, according to the latest figures, alarming the U.N. health officials, who long warned about the outbreak and the lack of proper response since it was reported in July.

The United Nations estimates the conflict has killed about 20,000 people and displaced millions.

The United Nations is concerned over the rapid spread of cholera in Sudan, where more than 600 people have died from the disease.