Barely half the $76 million requested for a six month programme proposed in July has been raised and the government and UN said in a statement that almost 2 million people needed food -- 200,000 more than estimated in July.
The situation has been worsened by heavy fighting in the south, the Taliban's stronghold, in what is already the bloodiest year since the group's government was driven from power by a US-led invasion in 2001.
They added the July plan needed to be expanded and continued until the next harvest in April.
"While we are grateful for the generous contributions received thus far, there is an urgent and pressing need to continue assistance to drought and conflict affected communities across Afghanistan," Deputy Special Representative of the UN Secretary-General Ameerah Haq said.
"We urge donor countries to step forward with pledges that will enable us to provide vital food and other essential living items as we approach the winter months."
In addition to those hit by the drought, more than 20,000 families have been displaced by fighting in the south.
Afghanistan, which relies on agriculture for more than half it's gross domestic product, has been in almost permanent drought since 1998, when the Taliban still ruled.
About 85 percent of crops rely on rain for irrigation.
Aid groups say about 2.5 million people in the north, central and southern regions are badly affected and some families have resorted to marrying their daughters off early to ease the burden on family incomes.
The latest figures are in addition to the 6.5 million of Afghanistan's population of more than 30 million who constantly or seasonally suffer a lack of food.
And Afghan leaders have warned the water shortage could drive more farmers to grow opium poppy, the raw material for heroin, which requires less water than most other crops, such as wheat.
The United Nations has estimated opium production will jump 60 percent this year in a country that already produces more than 90 percent of the world's supplies.

Copyright Reuters, 2006