Impoverished Yemen has descended into chaos in recent months, with a Shiite militia, known as Huthis, seizing control of Sanaa and forcing President Abedrabbo Mansour Hadi to flee to the main southern city of Aden.
The mounting unrest included suicide bombings claimed by the Islamic State group that killed 142 people in the capital Sanaa on Friday, and Washington moved to evacuate personnel as fears grow for the future of the country.
Benomar, who has tried to mediate the deepening conflict for several months, added that if immediate steps are not taken "the country will slide further into further violence and dislocation.
"In conclusion, I urge all sides in spite of rising tensions to appreciate the gravity of the situation and to deescalate by ceasing all hostilities and refraining from provocations and using violence.
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"Peaceful dialogue is the only way forward."
He also dismissed Hadi as "a puppet in the hands of forces of evil, led by the United States," and threatened to withdraw from UN-brokered dialogue between Yemen's multiple rivals.
The Arabian Peninsula country is increasingly divided between a north controlled by the Huthis, who are allegedly backed by Iran, and a south dominated by Hadi's allies.