The humanitarian crisis in Yemen has devolved into a "deepening catastrophe" with most of the country's population in desperate need of humanitarian assistance, three United Nations agencies said Friday.

The World Health Organization, UNICEF and the World Food Program said in a joint statement that the situation in Yemen has become "the worst humanitarian crisis in the world," and the reality on the ground is likely worse than current international assessments suggest.

Some 75 percent of the country's population is in need of humanitarian assistance, the agencies said. That includes 11.3 million children whose survival, the agencies say, is at risk without such aid. Sixty percent of Yemenis are food insecure, and millions lack access to basic sanitation and clear water.