After a year as the United Nations high commissioner for human rights, Mr. al-Hussein said he and many colleagues felt exhausted and angry at the overwhelming scale of humanitarian crises, singling out “the utterly shameful example” of the international community’s failure to address the conflict in Syria.

His account of the deepening crisis in Yemen echoed the findings of a report he released on Friday, which provided details about airstrikes by the Saudi-led coalition and about the shelling of civilian targets by the Houthis and their affiliated forces, among other violations, that it said might amount to war crimes.

Coalition airstrikes killed at least 941 civilians and injured 2,295 in May, June and July, according to the report. The air campaign, in conjunction with a naval blockade the coalition has imposed on Yemen’s main ports, had “dramatically worsened” the country’s humanitarian crisis, the report said.