by Ed Vulliamy in New York, Burhan Wazir and Gaby Hinsliff

International aid agencies have warned of a humanitarian catastrophe in the event of a war in Iraq, which could leave millions without food or shelter.

UNICEF, the children's charity, has already begun to move supplies to neighboring countries while the World Food Program is moving food it intends to provide for nearly a million people for one month. Aid officials say the United Nations' 'Oil for Food' program - under which tens of millions of Iraqis live on meager rations - would be suspended during any military action, leaving them facing starvation or reliant on emergency food aid.

The UN, which drew up a request at a meeting in Geneva last week for $37.3 million from donor countries to tackle the issue, is increasingly worried about the scale of any potential disaster.

In Britain, Clare Short's Department for International Development admitted last night that it was now holding 'regular discussions on general contingency preparedness' for a range of possible outcomes in the Middle East.

'In the case of Iraq, the UN is preparing for all such eventualities,' said a spokeswoman.

UN officials complain that the US administration is refusing to listen to warnings about the scale of the possible humanitarian disaster.

'There is a studied lack of interest in a warning call we are trying to deliver to the people planning for war, about what its consequences might be,' a UN official told The Observer yesterday.

The extent of Pentagon cooperation, say officials, is concern over the location of humanitarian sites and depots so as to try and avoid bombing them.

'In the light of the huge humanitarian consequences that could result, we will need full access to people in need,' said Mary McClymont of the umbrella group Inter-Action.

The planners who called last week's UN meeting said that conditions in Iraq 'after years of sanctions' are far worse than they were after the last Gulf war, with 'high levels of vulnerability and dependence'. The 1991 war caused more than a million Kurds alone to flee the fighting and an unknown number 'probably greater' of Southern Shia.

'All but the most privileged,' said the meeting's document, 'have exhausted their cash assets and in most cases their material assets'.

UNICEF has begun to move supplies to Iraq and neighboring countries, ready to provide for an initial half-million people inside Iraq and some 160,000 refugees outside its borders.

But the refugee agency, UNHCR, said it could only provide tents and blankets for 100,000. UNHCR, which acts as an umbrella organization in times of crises, is reeling from a 25 per cent budget cut globally for 2002. In the Geneva document the UNHCR says that it would take $60 million and six weeks to deliver tents and stoves suitable for winter conditions.

A spokesperson for Action Aid in London said war risked serious health problems in Iraq: 'In the event of a war, it is inevitable that the infrastructure which is already badly affected will begin to break down. And with that, you would see malnutrition and illness.'

Iran, Syria and Turkey have said they will take in Iraqi refugees if necessary. But a wider crisis might force other nations,including Jordan, to reassess decisions to keep their borders sealed.