Antonio Guterres, the secretary-general of the United Nations, has appealed for a cease-fire in all of the world's war zones, so countries can focus on fighting the coronavirus pandemic. Civilian populations in conflict-ravaged areas face the "highest risk of suffering devastating losses" from the virus, he said. Refugees and internally displaced people are "doubly vulnerable."

Guterres is right, of course: It is terrifying to think of the disease sweeping across, say, Syria, where years of fighting have devastated medical facilities - hospitals are a favorite target of the forces of the dictator Bashar Assad, and his Russian and Iranian patrons - and left millions displaced.

Sadly, however, Guterres' appeal may not have much if any impact on that case, or for that matter, in many others. But keep your eyes on Yemen, where his intervention could open a window for a settlement of its so far intractable conflict.

Worldwide, relief agencies are bracing for an outbreak in refugee camps, and Guterres is seeking $2 billion for an international humanitarian response. The U.N. refugee agency estimates that the number of people fleeing conflict exceeds 70 million, the highest level since World War II.

Alas, that number is no more likely to go down now than it was before the epidemic. If anything, some belligerents will use the coronavirus crisis to try and seize the advantage over others. To stick with the example of the Syrian conflict, the Assad regime, having acknowledged the country's first coronavirus case, could well push still more waves of refugees into Turkey, where the virus has already begun to take a toll.

But if Guterres were to concentrate on Yemen, he might have better luck. There, the belligerents might - just might - be sufficiently exhausted from years of fighting, to the point where he could bring enough pressure on the warring parties and their sponsors to halt the hostilities long enough for a humanitarian intervention to work.

It is now five years since a coalition of Arab countries launched a bombing campaign in Yemen, the opening salvo in a war that has turned one of the world's poorest nations into a humanitarian catastrophe. The coalition is led by Saudi Arabia, and its target is a rebel group, known as the Houthis, backed by money, training and arms from Iran.

According to the UNCHR's latest report on Yemen, 24 million people, or 80% of the population, are "in need," and more than 3.65 million are displaced. Unlike displaced Syrians, only a small proportion of Yemeni refugees have been able to leave the country; it is hemmed in by the sea on two sides, and its longest land border is with Saudi Arabia.

Yemen's heath system was poor before the war began; now, it is barely functional. Add to that widespread malnutrition and water scarcity in much of the country, and you have the perfect setting for an epidemic. Indeed, the country has already endured one - the world's largest cholera outbreak, in 2018, affected more than a million people, 25% of them children. The European Centre for Disease Prevention and Control says nearly 3,800 Yemenis have died from the disease.

As yet, Yemen has no "official" cases of coronavirus, but that means very little. The country is too poorly administered - whether by the Houthis from Sanaa or the internationally-recognized government in the south - for any reliable estimates. Ominously, the Houthis are preemptively blaming their enemies Worse yet, Houthi media outlets are parroting the line of their Iranian patrons that the coronavirus is an American biological weapon. On the other hand, the rebel government has taken the precaution of suspending schools and international flights.

Even so, relief agencies working in the country reckon that the spread of the epidemic is only a matter of time. Given their experience in dealing with the cholera crisis, they know the challenges coronavirus will bring. Gutteres himself has said he has "great confidence in our ability to adapt," but that sounds very much like whistling past the graveyard.

The secretary-general would better serve his relief staff, and Yemenis, if he spent the next few days pressing the protagonists of the war to put down their weapons and instead prepare for the crisis to come. This would require trips to Riyadh and Tehran.

To expect the Iranians, Saudis to do the right thing out of sympathy for the Yemenis would be too much. After all, they were not greatly moved by the cholera outbreak. But Guterres will likely find the leadership of the Arab coalition sympathetic for other reasons. Over the past year, the Saudis have shown a growing desire to exit their expensive, embarrassing Yemeni quagmire. The rebels, too, may welcome a break: Last fall, the Houthis and Saudis both signaled interest in a cease-fire.