In the cool desert dawn on May 16, at the Touloum refugee camp in eastern Chad, 2-year-old Fatima put her hands on her stomach, groaned and died. Her mother, Toma Musa Suleiman, in describing the death to me the next day, said that Fatima had been sick for 10 days. By the time she died, her skin was pallid and felt like plastic -- the effects of malnutrition.

I was seeing with my own eyes what I had been hearing about for several months: Children are dying almost every day in refugee camps in eastern Chad, despite a vigorous international effort to get food, water and other essentials to the more than 100,000 who have fled in fear from the Darfur region of neighboring Sudan.

They are among the 1 million Darfurians who have been displaced from their homes, most of whom are still in Sudan, according to aid groups.

Abukar Adam Abukar, a member of a community health team organized by Doctors Without Borders in the Iridimi refugee camp, one of half a dozen such sites, told me that seven children had died there between May 3 and May 14. He took me to the dusty flat on the edge of the camp where some of them were buried, in a forlorn line of small mounds of earth.

Why did Toma and thousands like her leave their homes and walk for days through the desert, risking their own lives and those of their children? Their stories were remarkably consistent. Person after person in the camps told me that they had fled after attacks on their villages by Arab Janjaweed militias, who have burned hundreds of villages and killed thousands of civilians belonging to black African ethnic groups. To make matters worse, the Janjaweed are backed by the Sudanese government, which wants to put down rebels drawn from those tribes. Many of the refugees said that the Janjaweed had stolen their animals and other property and that relatives or neighbors, usually men and boys, had been killed before their eyes. The refugees fled with little more than the clothes on their backs and the few things they could load onto a donkey. Many also said they were attacked from the air by the Sudanese government's Antonov bombers, either in their villages or as they fled toward the border.

I went to Chad last month on behalf of the U.S. Holocaust Memorial Museum's Committee on Conscience, which has issued a genocide warning for Sudan. Having now heard firsthand the refugees' accounts of the terror they faced in Sudan and of being driven into the desert, where their government is blocking assistance from the outside world, I have no doubt whatsoever that mass death will ensue in Darfur unless far more international assistance is immediately allowed to reach the displaced who are still there. In short, I fear the specter of genocide.

I interviewed refugees spread over hundreds of miles in eastern Chad. One woman, Hadiya Adam Ahmed, had crossed into Chad only two days before and was living under a tree near the remote border town of Bahai. Spread around her were her few remaining possessions: a blanket, some water jugs, a few bowls. She had left home without food and in two weeks of travel had depended on her fellow refugees for occasional handfuls of soaked sorghum for herself and her nine children. Hadiya had two bullet wounds in her right leg. She said she had been shot by a Sudanese soldier when she and a 17-year-old girl went to draw water from a well for themselves and others who were fleeing.

When asked why their villages were attacked and burned, most of the refugees said it was because of their black skin. They believe that the Khartoum-based government of President Omar Hassan Bashir wants to give their land to his Janjaweed allies who, like him, are Arab. Members of the Zaghawa, Masalit, Fur and other black African tribes will simply have to go. Like the Janjaweed, the Darfurians are Muslims. But culturally and ethnically they retain an African identity, of which they are proud. They also tend to be more settled than the nomadic Janjaweed. Racism undoubtedly does play a part in Bashir's support of the Janjaweed, as the blacks are seen as inferior.

Ironically, the prospects for peace in southern Sudan also contribute to the conflict. Fearing that an end to the generation-long rebellion in southern Sudan will divide access to the country's resources between the ruling elite in Khartoum and the southerners and condemn Darfur to permanent second-class status, some Darfurians launched an armed rebellion in early 2003. Khartoum responded by unleashing the Janjaweed and its own military on the black African civilian population. The result was what a team of U.N. investigators last month called a "reign of terror."

Those who have crossed into Chad are relatively lucky. An underfunded international relief effort by organizations such as Catholic Relief Services and Doctors Without Borders is providing some food, water, shelter and health care. For the displaced Darfurians who are still in Sudan, however, the situation is more dire. Khartoum has severely limited international access to them. And in the unforgiving desert, the stealing of food and animals, burning of homes and blockage of access to wells -- in short, the campaign of the Janjaweed and the government -- is tantamount to a death sentence. The U.S. Agency for International Development estimates that 350,000 Darfurians will die in the coming months unless the government in Khartoum allows international aid groups dramatically better access to the region.

That raises the question of genocide. Under the U.N. Genocide Convention, adopted in 1948 in the shadow of the Holocaust, genocide is defined as certain actions undertaken "with intent to destroy, in whole or in part, a national, ethnical, racial or religious group, as such." The actions include "killing members of the group," "causing serious bodily and mental harm to members of the group" and -- particularly relevant to Darfur -- "deliberately inflicting on the group conditions of life calculated to bring about its physical destruction, in whole or in part." The convention obliges parties to the treaty, including the United States and 130 other nations -- to "undertake to prevent and punish" the crime of genocide.

In cases like Darfur, there is always a great deal of hand wringing about what is and is not genocide. But such discussion misses the point: A key element of the Genocide Convention is prevention. It calls for action once it is apparent that genocide is threatened. There is no need for an absolute determination, which is inevitably elusive, that genocide is underway.

And in Darfur there can be no doubt that genocide is threatened. As former U.S. Ambassador David Scheffer once said of Kosovo, there are "indicators of genocide." Whatever the formulation, there is more than enough going on in Darfur to justify preventive action.

Time is of the essence. The rainy season will begin in the next few weeks, making access to Darfur -- where major roads become impassable with flooding -- difficult, if not impossible.

The government in Khartoum will do whatever it can to forestall any decisive international action. It is well practiced at giving the illusion of taking a step forward while really taking two steps backward. For example, it now is making a show of promising to streamline humanitarian access. But the record suggests that the government simply cannot be trusted. Even as it was claiming that the situation in Darfur was stable, its Janjaweed allies killed several dozen people on May 22. Allowing better access to aid groups will mean little if the militias continue to run rampant in the countryside.

What is needed now is a U.N. Security Council resolution mandating unrestricted humanitarian access to Darfur and laying the groundwork for the displaced Darfurians to return home safely. The Security Council should invoke the collective obligation to prevent genocide as well as its authority to maintain international peace and security, which is threatened by Janjaweed incursions into Chad and conflicts between the Chadian and Sudanese militaries. A statement issued by the Security Council on May 25, expressing "grave concern" about Darfur, is a step in the right direction. But it is no substitute for a formal resolution.

The United States has been lobbying in the Security Council, but it cannot do it alone. Darfur presents an opportunity for Secretary General Kofi Annan to avoid a repetition of the United Nations' failures during the Rwanda genocide of a decade ago, when warnings of mass murder were ignored. Indeed, in marking the 10th anniversary of the start of the Rwanda genocide on April 7, Annan said that reports from Darfur filled him "with a sense of deep foreboding."

Since then, however, he has said little in public other than to welcome Khartoum's promise to ease restrictions on international relief. His reticence is all the more remarkable because other U.N. officials, such as Mukesh Kapila, until recently the top U.N. humanitarian official in Sudan, have been outspoken in sounding the alarm.

Annan must say, simply, "This must stop" and use all his skill, energy and influence to forge an international consensus to back up that statement. To do otherwise, to welcome empty gestures from perpetrators of the gravest abuses, merely encourages them to continue to murder and pillage.

During both the Holocaust and the Rwanda genocide, warnings were received and ignored. Today we say "never again." The question now is whether we will ignore the warnings while the Africans of Darfur perish and then -- once again -- say "never again." Or will we act while lives can still be saved?

Jerry Fowler is staff director of the Committee on Conscience, which guides the genocide prevention activities of the United States Holocaust Memorial Museum.

Dislocation: In Farchana, Chad, about 30 miles from the Sudanese border, a camp was built in February for refugees from the Darfur region.Flight: Refugees fleeing fighting in Darfur traveled across the desert into Chad last January. An estimated 1 million people have been forced from their homes by militias backed by Sudan's government.Attack: Huts burned by militias two months ago in Bandago, Darfur, according to the World Food Program.Hunger: In mid-April, a Sudanese girl was admitted to a center for the malnourished in Mornay, Darfur.Grief: Mariam Bahar wept as she described the bombing of her village by Sudanese government forces in March.