Right now there is a rapidly growing fear among the international aid community. Already facing almost unprecedented demands from the fallout of the war in Syria, another humanitarian catastrophe has been slowly escalating elsewhere in the Middle East that has scarcely made the headlines.

I’m speaking of the war in Yemen which at this precise moment looks poised to slip into the abyss of a protracted, uncontrollable conflict. If the human cost of the Syrian conflict is enormous, then Yemen’s war is already as bad. It might come as a surprise to many who read this to realise that some 21 million people are in urgent need of assistance in Yemen right now. To put this in perspective, this is more than anywhere in the world, including Syria. As Europe reels in its efforts to support Syrian refugees coming here, it’s anyone’s guess as to how this refugee crisis might be compounded by those fleeing Yemen.

Before considering the full extent of this humanitarian disaster however, let’s pause to examine the latest military developments on the ground that have given rise to it. Yemen’s war after all is complex even by Middle East standards.

In short the main fight is between forces loyal to beleaguered Yemeni President, Abdrabbuh Mansour Hadi, and those allied to Zaidi Shia rebels known as Houthis, who forced President Hadi to flee the Yemeni capital, Sanaa in February for exile in the Saudi capital Riyadh.

Since then Saudi Arabia and other Arab states intervened in March to halt the nationwide spread of the Houthis who consider their rise a revolution, while the coalition fears the Houthis are bent on spreading the influence of Iran whose population – like the Houthis- is predominantly Shia.

This fear has brought together a coalition of Arab states which though headed by Saudi - Arabia also includes the United Arab Emirates (UAE), Morocco, Egypt, Sudan, Kuwait and Qatar. As if all this were not labyrinthine enough, the conflict has even more layers in terms of protagonists. To begin with it’s important to recognise that Yemen's security forces have split loyalties, with some units backing deposed Hadi, and others the Houthis and Hadi's predecessor Ali Abdullah Saleh. Adding even further to the complexity both President Hadi and the Houthis are opposed by al-Qaeda in the Arabian Peninsula (AQAP), who themselves are facing a challenge from the new jihadist presence in Yemen an affiliate of Islamic State (IS). As is so often the case these jihadists groups are hell-bent on exploiting the power vacuum caused by the wider war.

If you are still following all this, then as I write, the countries that make up the Saudi-led coalition are deploying personnel and equipment in preparation for a massive offensive on the Yemeni capital Saana.

Only yesterday coalition war planes were bombing Sanaa in what witnesses described as the fiercest attacks on the city in over five months.

The air strikes are reported to have hit houses of Houthi political leaders and terrified much of the city’s 2 million population among whom fear is spreading that an impending decisive battle in Sanaa will wreak widespread destruction, and add to the massive humanitarian crisis already gripping much of the country. As any aid worker in the region will testify, any further exacerbation is a dreadful prospect. If the offensive on Sanaa goes ahead then aid agencies will more than likely be forced to pull out staff altogether or have them go to ground while the worst of the fighting ensues. Every aid worker I have spoken to insists the impact of this would be devastating on what even before the war was the Middle East’s poorest country with one of the highest rates of child malnutrition in the world.

As UN humanitarian chief Stephen O'Brien, who has also just returned from Yemen, told the UN Security Council recently, "the scale of human suffering is almost incomprehensible". So far the UN’s World Food Programme has stopped just short of calling the humanitarian situation in Yemen a famine.

Aid agencies use the term sparingly and only declare a famine once certain conditions are met. These include over 20% of households in an area facing extreme food shortages with a limited ability to cope and acute malnutrition rates exceeding 30%. The death rate too must exceed two per day per 10,000 people. Such statistics of course say nothing about the suffering already being endured as a country teeters on the brink of an officially declared famine that meets these dreadful figures.

Already in Yemen conflict has spread to 20 of the country’s 22 provinces all this will change for the worst very quickly in the coming weeks if the military escalation goes ahead as expected.

Right now aid agencies are frantically trying to scale up their responses. The problem is that many of the country’s key ports have been blockaded or bombed by Saudi-led coalition airstrikes making the delivery of aid difficult and dangerous. The recent bombing of the port of Hodeida a crucial entry point for humanitarian supplies in the north and centre of the country has seriously impaired the aid effort at precisely the moment when people are almost out of water, food and medicine.

Recently according to satellite imagery gathered by the UN another seaport town Aden was shown to have more than 830 buildings damaged during four months of fighting. It is a small indication of what might lie ahead if the fighting now moves fully into the streets of the capital Sanaa. Over the last few weeks the world has woken up to the plight of Syria’s refugees. It might only be a matter of time before we will be faced with the same stark reality coming out of Yemen.