The war in Sudan could cost countless more lives if immediate action is not taken, as famine and disease spread while fighting intensifies and aid workers struggle to gain access, a senior World Health Organization official said on Tuesday.

Nearly 18 months have caused the world's biggest internal displacement crisis and more than 25 million people - over half the population of Sudan- are in desperate need of food and healthcare.

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"Malnourished children and mothers are dying due to lack of access to care, and cholera is spreading in many parts of the country. Aid workers face immense challenges," WHO regional director Hanan Balkhy told a briefing in Cairo.

"Without immediate intervention, famine and disease will claim countless more lives."

Estimates of the number of deaths run into tens of thousands but are highly uncertain, with control of the country split between the army and the rival Rapid Support Forces (RSF) and health facilities crippled.

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In the capital, Khartoum, 75 percent of health facilities are out of operation while the situation in the west and south of the country is worse, according to the WHO.

More than 20,000 cholera cases have been recorded this year in half of Sudan's 18 states, an outbreak spreading faster than another one in 2023, said Richard Brennan, a WHO regional emergency director.

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An oral vaccination campaign is due to start this week following the arrival of 1.4 million doses, with another 2.2 million doses expected later, he said.

The war between the factions began in mid-April 2023 after their rivalry burst into the open over internationally-backed plans for a transition towards civilian rule.