The donation was among the first prominent actions of the crown prince, the 31-year-old son of King Salman, since he was abruptly promoted to first in the line of succession on Wednesday, bypassing his older rival, Prince Mohammed bin Nayef, and upending decades of royal custom.
It was unclear whether the money was a direct donation from the personal fortune of the crown prince, who like other members of the royal family is enormously wealthy. But $66.7 million would not necessarily be considered an onerous sum for the crown prince, who as deputy crown prince spent $550 million in 2015 to buy a yacht from a Russian vodka tycoon.
Unicef and other humanitarian groups have expressed growing alarm about the rapid spread of cholera in Yemen, the Arab world’s poorest country, where the health care system has collapsed because of the war. A Saudi-led coalition began bombing the country more than two years ago after Yemen’s Houthi rebels seized the capital and evicted the Saudi-backed government.
The bombing campaign, which Crown Prince Mohammed has overseen as defense minister, has made only limited progress.
At the same time, the Saudis have faced growing criticism from human rights groups, which have accused them of indiscriminate bombings and air and sea blockades that have destroyed what is left of Yemen’s economy and worsened the humanitarian disaster there.
As many as 300,000 Yemenis could be infected with cholera in the coming weeks, half of them children, Unicef officials have said. Since the outbreak was declared two months ago, more than 1,265 people have died, Unicef’s resident representative in Yemen, Meritxell Relaño, told reporters in a conference call on Friday.
The Middle East regional director of Unicef, Geert Cappelaere, said last week that the agency had been so desperate to contain the cholera crisis in Yemen that it had taken the unusual step of paying the country’s doctors and nurses, who have not been paid in months.
Mr. Cappelaere said it was the worst cholera outbreak he had seen in Yemen and “just comes on top of what already was an incredibly daunting situation.”
Yemen is also facing a famine and a growing population of young children with severe malnutrition problems.
Cholera, once a common scourge of poor countries, is a bacterial disease spread by contaminated water that can cause fatal dehydration if left untreated.