"I think we do need to step up our efforts," said UN relief coordinator John Holmes, who has just returned from a visit to Afghanistan.
"I think we need to put together a new humanitarian action plan there, we need to mobilise more resources," he told reporters in Geneva.
He said the humanitarian situation in the country was "not only serious, but is also deteriorating".
An appeal for funds would be made in the coming weeks, he said. The actual sum was being finalised, but he estimated it would be around 300-400 million dollars.
Holmes said the appeal should cover assistance for 4.5 million people, including 2.7 million living in urban areas and the others in rural regions.
The package would include assistance in food, nutrition, health and development of agriculture.
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Afghanistan is facing a food shortage problem due to sharply higher food prices as well as a drought that is reducing the country's production of wheat -- a staple food -- by about 40 percent.
With more refugees returning from Pakistan and Iran, the country is also having problems resettling these displaced people.
At the same time, resurgent fighting is displacing people within the country.
Earlier Tuesday, officials said NATO and US troops killed dozens of militants on the Afghanistan-Pakistan border.
US-led helicopters and bombers killed 33 insurgents in eastern Khost province late Monday, while NATO soldiers in the same area co-operated with Pakistani troops across the frontier to kill several more rebels, they said.
But the violence came as the international troops passed a grim milestone: 49 soldiers died in June, making it their bloodiest month in Afghanistan since the fall of the Taliban and worse than Iraq for the second month in a row.
© 2008 Agence France Presse