“We need to reassess every single thing we are doing as to what we can do to bring an end to this conflict,” added Mr. Beasley, a former governor of South Carolina who was appointed to lead the agency by the Trump administration in March.
By making Riyadh, the Saudi capital, the first stop on his tour, observers say, Mr. Trump has signaled a desire to strengthen ties that were strained under the last administration. To underscore that intent, officials in Washington say the administration is poised to complete more than $100 billion in weapons sales to Saudi Arabia.
The deals, which could reportedly total $300 billion over 10 years, have led to criticism that the United States is supporting Saudi military operations that have struck hospitals, schools, markets and mosques and inflicted thousands of civilian casualties.
United Nations and other human rights officials say Houthi rebels and affiliated forces have also shown disregard for civilians with indiscriminate rocket and artillery bombardments of residential areas, sniper fire and land mines.
The State Department and other United States government agencies have tried to limit the effects of the hostilities, with little success. Their interventions have included efforts to protect the western port city of Hudaydah, a crucial lifeline for food and medicine entering the country, from attack, Mr. Beasley said. “I was hopeful two weeks ago that was about to resolve, but evidently that hasn’t happened,” he said.
“This is a colossal failure of international diplomacy and a colossal failure to get out the message of a crisis that is now of biblical proportions,” Jan Egeland, the Norwegian Refugee Council head who visited Yemen this month, said in an interview.
“This is a clear-cut decline into massive famine that is man-made and avoidable,” he said. “There has to be leadership from United States and Britain to get a real peace process going.”
A Yemeni child dies every 10 minutes from malnutrition or related causes, United Nations agencies report. But deliveries of food, medicine and other essential supplies have slowed, Mr. Egeland said, because the coalition’s screening of shipping is delaying arrivals, war damage to the cranes at the Hudaydah port is hindering unloading, and the country’s public and private financial reserves are exhausted.
Hunger and desperation are reaching levels that make public distribution of food relief increasingly risky, he said. Yet on a visit to one of the main hospitals in Sana, he found the emergency feeding center in the process of discharging patients and closing down because staff members had not been paid for eight months.
The World Health Organization has reported that less than 45 percent of the country’s hospitals and clinics are fully functional, and that many lack access to clean drinking water, creating conditions ripe for the spread of disease.
The number of cholera cases has exploded in the past two weeks, overwhelming medical facilities, Marie Claire Feghali, a spokeswoman for the International Committee of the Red Cross in Geneva, reported.
Visiting two of Sana’s main hospitals on Sunday, Dominik Stillhart, the committee’s director of operations in Yemen, saw beds crammed with up to four patients, and others hooked up to intravenous drips in cars parked outside because of the lack of space.
After 40 years dealing with international aid and humanitarian relief operations, Mr. Egeland said, “I’m more worried for Yemen now than for any other place on the planet.”