The World Health Organization (WHO) warned on Friday that cholera cases in Sudan are set to rise and could spread to neighbouring countries, including Chad, which hosts hundreds of thousands of refugees from Sudan's civil war in crowded conditions.

The more than two-year-old war between the Sudanese army - which took full control of Khartoum state this week - and the paramilitary Rapid Support Forces has spread hunger and disease and destroyed most health facilities. Drone attacks in recent weeks have interrupted electricity and water supplies in the capital Khartoum, driving up cases there.

"Our concern is that cholera is spreading," Dr Shible Sahbani, WHO Representative for Sudan, told reporters in Geneva by video link from Port Sudan.

He said that cholera had reached 13 States in Sudan, including North and South Darfur which border Chad, and that 1 854 people had already died in the latest wave as the dangerous, rainy season sets in.

"We assume that if we don't invest in the prevention measures, in surveillance, in the early warning system, in vaccination and in educating the population, for sure, the neighbouring countries, but not only that, it can maybe spread to the sub-region," he said.

He called for humanitarian corridors and temporary ceasefires to allow mass vaccination campaigns against cholera and other disease outbreaks such as Dengue fever and malaria.

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

Sahbani said that this posed a high risk for Sudanese refugees, including some who had survived attacks on a displacement camp in Darfur, and who are living in cramped, makeshift border sites on the Chadian side of the border.

"In overcrowded, unsanitary conditions, a potential outbreak could be devastating," said François Batalingaya, UN Resident and Humanitarian Coordinator in Chad at the same briefing, describing the conditions for some 300 000 people stranded there with few aid services due to funding shortages.

The disease has not yet been confirmed in Chad, although a WHO spokesperson said that suspected cases had been reported in Geneina, Sudan which is just 10 km away. Sahbani also said that disease surveillance was low on the Libyan border and that it could possibly spread there.

Case fatality rates have fallen in recent weeks in and around the capital Khartoum thanks to an oral cholera vaccination campaign that started this month, Sahbani said.