Hans Grundberg pointed to military build-ups and threats along frontlines as signs the fragile pause in fighting is collapsing. The Houthis have attacked more than 80 merchant ships since the Gaza war began, and a cholera outbreak has grown to more than 147,000 cases with funding covering only a quarter of them.
The Houthis seized the port city of Mocha and several key positions near Taiz in September, unravelling a ceasefire that had largely held for four years. Officials fear a return to full-scale war in one of the country's most densely populated areas.
Flames rose from an Aramco facility south of Riyadh on Saturday, with the Houthis saying they had hit it with missiles and drones. The exchange comes as the World Food Programme warns that three-quarters of Yemen's population cannot meet basic food needs.
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