A cholera outbreak in Sudan could get worse as war, displacement and the onset of the rainy season threaten to exacerbate a humanitarian crisis in the country, the World Health Organization warned on Friday.

The cholera outbreak declared on June 27, which has killed at least 114 people and infected more than 1 300 others, is spreading across several Sudanese states, particularly in Darfur and Kordofan, where access for aid and healthcare workers remains severely constrained, the WHO said.

"Cholera is back," the WHO representative in Sudan, Shible Sahbani, told reporters in Geneva via video link from Libya.

"There is (a) case fatality rate of 13.7%, which is extremely high, and of course, the rainy season is expected to worsen the situation," Sahbani added.

Cholera is a severe and potentially fatal diarrhoeal disease that spreads quickly when sewage and drinking water are not adequately treated.

Sudan faces the world's largest humanitarian emergency, with more than 33 million people in need of assistance and 21-million requiring health services, according to the WHO.

Sahbani expressed particular concern about the situation in the besieged city of al-Obeid, the capital of North Kordofan, where health facilities are overwhelmed and humanitarian access is difficult amid intensifying fighting between Sudan's army and the paramilitary Rapid Support Forces (RSF).

A United Nations official warned earlier this month that a human rights catastrophe was unfolding in the city, similar to that seen in al-Fashir, ​in north Darfur, which the RSF captured last year after a long siege.

"There is the risk that it will become the second al-Fashir, or even worse," Sahbani said.