Confirmed cholera cases jumped past 1,400 across returnee transit sites in Iran’s Ilam province and Iraq’s Diyala and Maysan governorates this weekend, the World Health Organization said Sunday, as damaged water-treatment plants and overcrowded transit camps fueled the first large outbreak of the post-ceasefire phase.

The WHO’s regional office in Cairo, citing reports from health authorities in both countries through Saturday night, said 1,432 cases had been laboratory-confirmed or were being treated as probable cholera, with 19 deaths recorded so far. More than two-thirds of the dead were children under five or adults over sixty, and case counts had roughly tripled in the past four days.

“This was the outbreak we have been warning about for two weeks, and it has arrived faster and broader than our baseline modeling,” said Dr. Hanan Balkhy, the WHO’s Eastern Mediterranean regional director, in a video briefing from Cairo. “We are still in the early ascending phase of the curve. Without an immediate scale-up in clean water and oral rehydration capacity in the affected districts, we are going to see this double again.”

The outbreak’s epicenter is the Mehran-Khanaqin corridor, where roughly 260,000 displaced people from both sides of the border have been moving through transit sites since the April 15 ceasefire took effect. Iraqi health officials in Baquba said the largest single cluster had emerged at the Karim Khan reception camp outside Khanaqin, where more than 11,000 returnees had been waiting for road clearance and mine-survey teams to certify routes deeper into Diyala. A second cluster was identified Friday at a smaller site near Badra, on the Iraqi side of the Mehran crossing.

On the Iranian side, the provincial health directorate in Ilam confirmed at least 480 cases distributed across four transit and reception points, including one at the badly damaged outskirts of Mehran itself. Iranian state media reported that emergency teams from Tehran had been redeployed to the area and that the country’s national pharmaceutical company had been ordered to fast-track production of oral rehydration salts and intravenous fluids.

Public-health officials traced the most likely source of the outbreak to two water-treatment plants knocked offline during the war’s middle weeks — one struck directly during an air campaign in late March and a second taken out of service by a power-grid failure that has not been fully repaired. Both plants normally serve more than 400,000 people across the cross-border corridor, and their absence has pushed transit camps onto untreated wells and informal tanker deliveries of uncertain provenance.

“The bacterium does not care about borders, and right now neither does the contamination,” said Dr. Karim Soltani, an epidemiologist with the WHO’s Tehran country office, by phone from Ilam. “We have shared aquifers, shared rivers, and people moving back and forth in numbers we have not seen in a generation. The only thing that stops this is clean water, fast, and we do not have enough of it.”

UNICEF on Sunday said it had begun airlifting cholera kits, intravenous fluids and roughly two million sachets of oral rehydration salts from its regional warehouse in Dubai, with the first cargo flights expected to land at Baghdad and Kermanshah on Monday. The agency said it had also activated standby contracts for the rapid deployment of mobile water-treatment units capable of producing about 90,000 liters of safe drinking water per day each, and was working to position eight of them across the affected districts by midweek.

A coordinated vaccination campaign is now under preparation. The International Coordinating Group on Vaccine Provision, which manages the global oral cholera vaccine stockpile from Geneva, told donor governments on Saturday that it had approved an initial release of 1.6 million doses for the corridor, drawn from a stockpile that has been under sustained pressure from outbreaks elsewhere over the past year. The first doses are expected to begin moving from Lyon early next week, with priority given to children and elderly returnees in the largest reception sites.

The outbreak is also raising fears that the post-war phase will be defined as much by disease as by reconstruction politics. A senior State Department official, speaking on condition of anonymity to discuss internal assessments, said Washington was watching the corridor “with a level of concern that is going beyond what the planning assumptions told us six weeks ago.” The official said the administration was reviewing whether to release additional humanitarian funding above the supplemental request currently before Congress.

“You cannot rebuild a region while you are burying its children,” said Layla Hassan, a Beirut-based regional analyst who has tracked recovery operations across the Levant for almost two decades. “Every dollar that goes into water and sanitation in the next thirty days will save more lives than almost anything else donors are funding right now.”

The Iraqi Health Ministry, in a statement Sunday evening, said it had ordered all elective surgeries postponed in district hospitals across Diyala and Maysan and was redirecting staff from Baghdad and Basra to the affected areas. Iranian authorities, in a parallel statement, said schools in three districts of Ilam would remain closed for at least an additional week and that mobile clinics had been authorized to operate around the clock at the largest reception sites.

International humanitarian agencies have urged governments not to halt the broader returns process despite the outbreak, arguing that conditions inside long-running displacement camps further from the border are themselves deteriorating. UNHCR said on Sunday that it would maintain its current phased schedule but tighten medical screening at transit points, with cholera-specific protocols added to existing checks for measles and acute respiratory illness.

The WHO said a fuller field assessment, including projections for case counts over the next three weeks and an updated funding appeal, would be presented to donor governments at a coordination meeting in Amman early next week.