The food-crisis forecasting agency created by the United States has added its voice to warnings of imminent and widespread famine in Yemen because of the Saudi-led blockade, now more than two weeks old.

The American alert on Yemen, from the Famine Early Warning Systems Network, said that a prolonged closure of key ports in Yemen “risks an unprecedented deterioration in food security” to its worst category, Phase 5, “across large areas of the country.”

The five-stage scale — with Phase 5 being famine — is used by humanitarian aid groups to anticipate the severity of potential hunger emergencies. Famine is defined as existing in areas in which at least one in five households suffers “an extreme lack of food and other basic needs where starvation, death and destitution are evident.”

Relief officials of the United Nations and other humanitarian groups have said at least seven million people are at risk of famine in Yemen, the Arab world’s poorest country, because of restrictions on deliveries imposed by the Saudi-led military coalition that has been fighting Yemen’s Iran-backed Houthi rebels since 2015.