GENEVA - The World Health Organization warned Friday that a Saudi-led blockade of Yemen was threatening to undo efforts to rein in a cholera epidemic already affecting nearly one million people in the war-ravaged country.

Yemen , where a multinational conflict has caused a daunting humanitarian crises, has seen nearly 914,000 people infected by cholera since the latest outbreak began in April, according to WHO figures.

Nearly 2,200 people have so far died from the waterborne disease, which has propagated rapidly due to deteriorating hygiene and sanitation conditions.

A massive vaccination campaign had in recent weeks helped slow the spread, but WHO spokeswoman Fadela Chaib warned the Saudi-led coalition's decision to seal off Yemen 's borders this week threatened the progress made.

"We will suffer a major setback if we don't have full access to all affected areas," she told reporters in Geneva. "Controlling the cholera outbreak is a very difficult challenge... Certainly closing borders and all access to the country will not help," she said. Saudi Arabia and its allies intervened in neighbouring Yemen in March 2015 with the stated aim of rolling back gains by the Iran-backed Huthi rebels and restoring the government of Abedrabbo Mansour Hadi to power.

The coalition has since the beginning enforced a de facto blockade on land crossings and air and sea ports, and the UN and other international humanitarian organisations are required to take permission for sporadic aid deliveries.

The blockade was tightened further on Monday, when the coalition said it was closing Yemen 's borders and ports to aid agencies, after Saudi Arabia accused Iran of being behind a rebel attack in which a missile was intercepted near Riyadh airport over the weekend.

The UN Security Council demanded Wednesday that the blockade be lifted, amid warnings of mass famine.

Chaib echoed that call, pointing out that cholera was "all over the country."

"We need to have unlimited access to all governorates of Yemen to be able to move, to be able to provide assistance to the health centres and hospitals."

The UN children's agency UNICEF also warned of dire health consequences if the blockade continues.

Maritxell Relano, head of UNICEF's operations in Yemen , pointed out that fuel was about to run out.

"The current stocks of fuel will only last until the end of November, and we need fuel to maintain the health centres open and the water system functioning," she told reporters in Geneva via conference call from Yemen .

"The operative water supply systems and the water treatment plants will stop if we don't have fuel, so the risk, the impact is unimaginable in terms of health (and) diseases," she cautioned.