The possibly catastrophic combination of food shortages and lack of security is most severe in northern Afghanistan, where three factions of the Northern Alliance are jockeying for power, the officials say.
Citing concerns about tensions among the factions, the U.N. withdrew its sole foreign staff member this week from Mazar-i-Sharif, which was seized from the Taliban on Nov. 9. The International Committee of the Red Cross and other aid agencies, however, are not discussing leaving.
In the past, tensions among the ethnic groups that make up the alliance have escalated into large-scale bloodshed, but there appears to be no evidence of open conflict in Mazar-i-Sharif at the moment.
U.N. security officials said privately that they are also concerned about a number of Taliban soldiers who are unaccounted for and may be roaming areas of the north since the fall of Kunduz, their holdout city in the region.
"Unless the security situation improves in the north, more people are going to suffer during the winter months," Antonio Donini, deputy U.N. coordinator for Afghanistan, said Tuesday by telephone from Islamabad, Pakistan. "And there will be people dying of hunger in numbers that are impossible to quantify, but potentially large numbers."
With winter already upon the country's highlands and the continued fighting hampering delivery of food and supplies in the north and west, Afghanistan faces its worst humanitarian disaster in 30 years, Afghan exiles in Iran and leaders inside the country say.
Those Afghan leaders predict that 2 million Afghans risk death from starvation and exposure in the coming months despite the international aid pouring into the war-decimated country.
Six million to 7 million people in Afghanistan depend either completely or in part on foreign aid to survive, the U.N. estimates.
The U.N.'s security officers have judged only three cities safe for the return of the organization's foreign staff: Kabul, the capital, where about 30 foreign U.N. staff members now work, and Herat and Faizabad, each of which has about seven foreign U.N. workers.
The U.N. ordered its field security officer doing an assessment in Mazar-i-Sharif to leave the city "because a few days ago the situation in town was very volatile," Donini said.
Although he said security has improved slightly in Mazar-i-Sharif in recent days, U.N. officials speaking on condition of anonymity said a simmering rivalry within the Northern Alliance could erupt at any time in the city and the surrounding area.
Most often at odds are the Jamiat-i-Islami faction that dominates the alliance; Uzbek warlord Gen. Abdul Rashid Dostum, who for years treated the area as a personal fiefdom; and the Hezb-i-Wahdat, which sees itself as the defender of a persecuted minority, the Hazaras.
The Hazaras have complained that they aren't properly represented at talks in Germany aimed at creating a power-sharing interim administration for Afghanistan. But publicly at least, Hezb-i-Wahdat leaders have said they are willing to give the peace process a chance to create a truly broad-based government.
The draft agreement reached in Bonn includes deployment of an international security force in Kabul and the surrounding area. But the Northern Alliance has said the force will be responsible for protecting members of the interim authority, not keeping the peace in the rest of the country.
A decision on requesting a larger international force may be made by the interim authority once it takes power, but many Afghans are wary, fearing it might become an occupying force that tries to dictate a political solution.
"In the future, if these [Afghan] parties join in the government and there is no interference from neighboring countries or outside powers, they will be able to provide security," said Mohammed Ebrahim Nazhand, national representative for CARE International in Kabul. "There will be no need for a foreign force."
CARE has a variety of aid and relief programs in Afghanistan, from supplying potable water to tens of thousands of people in Kabul to repairing houses ruined by war in various parts of the country.
The agency's Afghan staff had remained in the crossroads southern city of Ghazni during the U.S. airstrikes, but they were forced to pull out last week, officials said, because the Taiban's collapse left a dangerous power vacuum.