The United Nations has opened a third pledging conference in hopes of drumming up some $4 billion this year for Yemen, a war-battered country facing the world's worst humanitarian crisis.

Host U.N. Secretary-General Antonio Guterres lamented "an overwhelming humanitarian catastrophe" where some 24 million people, or four-fifths of Yemen's total population, require aid and protection.

"Twenty million people cannot reliably feed themselves or their families," he said in Geneva, where the meeting is taking place. "Almost 10 million are just one step away from famine."

U.N. officials say they are running out of money in a country also facing a devastated health care system, a lack of jobs, continued fighting and fallout from the world's worst cholera epidemic in 2017.