The warning of a building humanitarian catastrophe in the Ivory Coast comes amid alerts that heavy weapons could be used as the nation's rival presidents fight for power.
Forces loyal to current president Laurent Gbagbo are preparing to use an attack helicopter and multiple rocket launchers against ordinary people, the United Nations said yesterday.
It called the weapons "a grave threat to the civilian population" and warned Gbagbo forces that the UN would act if these weapons are used.
The west African country has been terrorised by fighting between forces loyal to Gbagbo, who is refusing to step down as president after a contested election, and those of his rival, Alassane Ouattara.
The UN recognises Mr Ouattara as the winner of the November election.
About 500,000 people have fled the fighting there - but a UN appeal for aid money to help them has largely gone ignored. An appeal for £20m has brought in just under £5m so far.
"With the deteriorating situation in Ivory Coast we would like to make a new appeal to donors," said the UN's Elisabeth Byrs, calling the shortfall in funding "unacceptable in view of the situation."
The World Food Programme is also struggling to find the cash to help those who have fled.
"We've been calling on our donors really to understand that they have to pay attention to all the crises going on in the world." said the food programme's Emilia Casella.
"This is an extremely trying time for everyone, but if we cannot get funding for our Ivory Coast and Liberia operations now, we are not going to be able to buy the food and acquire it for the people who need it, even three or four months down the road."
After at least 25 people were killed when a market in the country's former capital, Abidjan was shelled last week, aid workers say the city is emptying as people, many of them women and children, desperately try to flee. Most are taking nothing with them.
And the UN has hardly anything to give them as the country rattles into what some are already calling civil war.
More than 435 people have been killed in the post-election violence, according to the UN. And about 90,000 people have fled to neighbouring Liberia and some 300,000 have fled Abidjan, aid groups say.