-- Nearly three-quarters of a million displaced Afghans are struggling to survive freezing temperatures in refugee camps with scare supplies in various parts of Afghanistan and Pakistan, prompting the United Nations to warn that many face imminent death unless drastic steps are taken to alleviate their misery.

An estimated 500,000 homeless people are huddled in frozen camps in western and northern Afghanistan, according to U.N. officials. Another 180,000 have crossed into Pakistan, where many are being housed in camps in that country's rugged northwest. In addition, relief officials say, an unknown number of other displaced Afghans may be wandering their country without food or shelter, or struggling with the effects of drought and economic hardship at home.

"We believe at least 1 million people are at risk of famine," Kenzo Oshima, undersecretary general in charge of the U.N. humanitarian affairs office, said Tuesday in Geneva after he returned from touring camps for displaced people in Afghanistan. "I saw a sea of people living in unbelievable misery."

Oshima said international assistance to the refugees was urgent and the situation "threatens to become a major humanitarian catastrophe." In one camp in the western Afghan city of Herat, he said, he saw a graveyard "full of small, new graves of children."

The refugees' plight has been caused partly by a severe drought that has affected Afghanistan for the past year, killing large herds of cattle and sheep and rendering vast areas of cropland unusable, especially in the dry southern regions.

At the same time, a protracted civil war between Afghanistan's ruling Islamic militia, the Taliban, and opposition forces based in northwestern and central Afghanistan has driven hundreds of thousands of people from the north, where fighting and bombing have destroyed hundreds of villages.

In the past several months, nearly 80,000 people have reached the Herat area, where they are huddled in six camps under makeshift tents with little to eat. Temperatures have fallen below zero on some nights, and U.N. officials estimate that about 150 people, mostly children, have died from cold.

"Unless more food and aid can be delivered to remote villages, I expect the total number of displaced persons [in Herat] may go beyond 100,000 this spring," said Hans-Christian Poulsen, the United Nations' regional coordinator for western Afghanistan. During December and January, he said, 500 people a day arrived in Herat.

In north and central Afghanistan, tens of thousands of people are living in camps in areas controlled by the Northern Alliance, the armed group that opposes the Taliban. Some have tried to flee north to Tajikistan but have been turned back, and about 12,000 are stranded on two islands in a river that divides the neighboring countries. "As far as we are concerned, this is a war zone," one U.N. official said in Tajikistan recently.

The United Nations is providing food and rudimentary shelter to the refugees, but the Tajik government refuses to let them cross the border. "They feel if they let these refugees in, there could be another 150,000 close behind," the U.N. official said. "It would be taking the cork out of the bottle."

Refugees who have reached camps inside Pakistan are in relatively better conditions, but 15 children died there from the cold last week. With about 700 people still crossing the border daily, officials from U.N. refugee and food programs said they are reaching the limits of their supplies of food, tents and other emergency needs while aid from foreign donors has dropped sharply.

Officials of the Taliban have asked for extra U.N. assistance, saying they have virtually no resources to help the internally displaced population. Afghanistan is bankrupt after two decades of war, and the regime has been economically and diplomatically isolated since taking over in 1996 because of its draconian religious policies and support for international terrorism.

Last month, the U.N. Security Council imposed new economic sanctions on the Taliban, which included an arms embargo and limits on the travel and foreign missions of its officials. The United Nations has demanded that the Taliban hand over Osama bin Laden, a wealthy Saudi fugitive and Islamic radical whom U.S. officials accuse of masterminding several foreign bombings, but it has refused.

Taliban officials have protested that the sanctions are inflicting further hardship on the general populace at a time of great need. But U.N. officials said they were aimed only at the government, while the U.N. humanitarian arm is providing food, shelter and medicine for hundreds of thousands of Afghans.

In a goodwill gesture two weeks ago, the Bush administration sent a planeload of relief supplies to Herat, including several thousand blankets and tents. The U.S. government does not recognize the Taliban and recently shut down its diplomatic office in New York under the new sanctions.

The United Nations has made several urgent appeals for aid to Afghan refugees and displaced people in the past several months. But officials said the response has been small, largely because donor countries are weary of the long-term Afghan crisis, which has sent more than 5 million refugees to Iran and Pakistan over the past decade.

A U.N. report last month said that even if conditions improve in Afghanistan, many refugees would not be able to return home because they had sold their "last remaining assets," including farm tools and animals, and have no seeds to plant.

Fahim, an Afghan refugee, sits with his children in a U.N. refugee camp near Peshawar. It is estimated that 180,000 people have fled into Pakistan.Afghan women and children wait for food at a new camp near Peshawar where they endure bitter cold and primitive living conditions.Hundreds of displaced people wait for help outside the World Food Program distribution point near Herat in western Afghanistan.