Donors in April pledged close to USD 1.1 billion (981,500 euros) in aid to war-torn Yemen, which the UN Office for the Coordination of Humanitarian Affairs calls the "largest humanitarian crisis in the world".
But "only 25 per cent of aid pledged to the UN refugee agency and 29 percent of aid pledged to the UN's humanitarian response plan have been delivered so far," UNHCR's Yemen spokesperson Shabia Mantoo told AFP.
Yemen's deadly war has seen more than 8,000 people killed and millions displaced since a Saudi-led Arab coalition intervened to support a government fight against Shiite Huthi rebels allied with Iran.
Looming famine and an outbreak of cholera in Yemen, the most impoverished country long before the war, are taking their toll on the population.
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"Conditions are only worsening. The cholera rates are alarming, health facilities are struggling to remain functional, millions across the country are food insecure and facing prolonged displacement from their homes," Mantoo said.
A quarter of a million people are expected to contract cholera within six months, according to the World Health Organisation.