IN A SPEECH on the 10th anniversary of the Rwandan genocide, U.N. Secretary General Kofi Annan pleaded that, in the face of the genocide that now appears to be occurring in the western Sudanese province of Darfur, "the international community cannot stand idle." Five weeks later, Mr. Annan's plea has been underlined by reports from the region. On Friday, Human Rights Watch published a detailed account of the systematic destruction of villages and the killing "in cold blood" of thousands of civilians, whose bodies have been shoveled into mass graves or simply left out in the sun. The killings were perpetrated by Sudan's government, in concert with its allies in the Janjaweed militia. They constitute a grotesquely exaggerated response to a regional rebellion that started a year ago to protest the neglect of Darfur's ethnically African population by the Arab government in Khartoum.

Unless Mr. Annan's plea is heeded, things are about to get worse. As many as 1 million inhabitants of Darfur have been driven from their homes; they have no access to the fields they should be planting at this time of year. Soon the rainy season will begin, and it will be too late for planting; it will also become a lot harder for relief organizations to bring in food by truck. There have already been outbreaks of meningitis in the refugee camps, and child deaths from malnutrition are rising. Human rights groups describe the refugee camps as de facto prisons: They are ringed by militiamen who attack women venturing out for firewood. These prison camps will become death camps if nothing is done to supply them.

Like many civil wars, this one threatens to suck in its neighbors. The Janjaweed militia members have mounted raids on refugee camps in Chad, where more than 110,000 fugitives from Darfur have sought sanctuary. They have been backed by Sudan's government, which has sent helicopters to support them. On Sunday, Chad's government declared that its army would fight back against the marauders, and it reported on a skirmish in which dozens had been killed. Just as Rwanda's genocide triggered war in Congo, and just as Sierra Leone's civil war spread to its neighbors, the current atrocities in Darfur may have regional consequences.

Until now, the Western governments that have leverage over Sudan have not wanted to use it. They are brokering a peace between the government and the southern rebels and believe that pressuring the government on Darfur would use up scarce bargaining chips. But however important the north-south peace process is, the Darfur crisis should not be marginalized. The violence there is too atrocious, and unless Sudan's government proves itself serious about implementing the Darfur cease-fire to which it has theoretically agreed, it's hard to believe that a peace treaty with the south would really mean much. The United States and its allies should insist that the Sudanese regime rein in its militia; that it cease all joint operations with them; and that it allow humanitarian organizations immediate, red-tape-free access to the region.