Painting a dire picture to world powers on Wednesday about life in Yemen, a United Nations envoy warned that polio could soon make a comeback and that a dengue outbreak had struck an estimated 3,000 people.

Clean drinking water is out of reach for 20 million - most of Yemen’s population - and a large portion of country is, in the words of the envoy, “one step away from famine.”

The envoy, Esmail Ould Shaikh Ahmad, the special mediator for resolving the Yemen conflict, spoke to Security Council diplomats in a closed meeting on Wednesday morning. Later in an interview, Ould Shaikh Ahmad said he was continuing to push for a humanitarian truce during the holy month of Ramadan between the Saudi-led coalition carrying out air strikes and the Al Houthi militiamen who have ousted the Saudi-backed government.

But important hurdles remain, he said. The Saudi-led coalition insists on two things before agreeing to any humanitarian cease-fire: the withdrawal of Al Houthis from strategic cities, and monitors on the ground, to ensure that a truce is not broken as it has been before.

Al Houthis, for their part, he said, have yet to agree to withdraw, arguing that extremist groups would step into the breach. The militants have taken control of vast areas of the country. But the envoy insisted that any truce deal would require that they agree to pull back.

“The current situation is unsustainable. You cannot go as any movement in any country and start occupying the cities one after the other,” he said. “Even if you have political grievances that’s not the best way.”

Ould Shaikh Ahmad, a Mauritanian diplomat, faces the additional challenge of recruiting UN civilian monitors to observe any such truce.

Humanitarian aid is trickling into the country, but it cannot come close to meeting the need, especially for food and fuel, aid officials say. Water pumps cannot run without diesel, and civilians have a difficult time reaching health clinics. Yemen, the poorest country in the Arab world, imports most food and fuel.

The UN humanitarian coordinator, John Ging, said 80 per cent of Yemen’s population now depended on aid and that a near halt in food and fuel shipments had caused the humanitarian crisis to accelerate “at a very rapid rate.”

His Office for the Coordination of Humanitarian Affairs has for more than two months tried to work out a verification mechanism to assure the Saudi-led coalition that weapons do not come in with civilian commercial goods. They have not yet agreed on a plan.

At the closed-door session on Wednesday, Ging appealed to the council to help persuade the Saudis to enable the United Nations to set up a what diplomats called a “light and efficient” verification system.