When foreign ministers from major countries meet in Geneva on Thursday to address the horror in Darfur, they must demand in no uncertain language that Sudan's government stop the ethnic cleansing there.

A million people have been chased from their homes in the west of Sudan; untold thousands have been murdered or raped. Hundreds of thousands face imminent death from starvation and disease.

The public knows little about their plight because the Sudanese government has been refusing visas to humanitarian workers and journalists, and entering Darfur over the border from Chad is risky. But the Darfur crisis is just as pressing as Bosnia in 1993, if not more so. The United Nations recently called it the world's biggest humanitarian disaster.

The foreign ministers meeting in Geneva should commit generous resources for humanitarian relief and human rights monitoring; insist on unhindered access; demand that the appointed UN humanitarian coordinator be allowed to take up his post, and ensure that humanitarian programs do not inadvertently promote ethnic cleansing.

But they must not stop there.

As in Bosnia, the people of Darfur need foreign aid so desperately because armed forces have been committing crimes against humanity in their villages. Unless those crimes are stopped, reversed and punished, the humanitarian crisis will continue.

Left to its own devices, the Sudanese government will not stop those crimes; on the contrary, it is sponsoring them. Deploying militia known as Janjaweed with the backing of government troops and aircraft, it has pursued a scorched-earth campaign against the members of three African ethnic groups. Hundreds of villages have been left in smoking ruins.

Intense international pressure is needed to force the government to end these atrocities and permit the displaced to return home.

Last week, Human Rights Watch and others briefed the UN Security Council, the body most capable of putting pressure on Sudan. We told of the deadly campaign in Darfur. We described the remedial steps needed. Council members listened attentively. But their public statement fell short of what is needed.

When the Security Council wants to insist on action, it adopts a mandatory resolution under Chapter VII of the UN Charter. But in the case of Darfur, it issued only a nonbinding statement. Instead of "demanding" action, it politely "urged" it. It did "condemn" the atrocities - a useful step. But it didn't even name the perpetrator, as if these government-directed atrocities were somehow spontaneous eruptions.

Sudan's government undoubtedly noticed these distinctions. A few days later, on May 28, its aircraft attacked a village in northern Darfur on market day, killing at least 12. In a weeklong spree that coincided with the Security Council statement, 3,000 Janjaweed were reportedly marauding in southern Darfur, burning villages and killing civilians, apparently heeding President Omar al-Bashir's plea to "secure" the area. These atrocities make a mockery of a cease-fire agreement reached on April 8.

Western governments are filled with excuses for why more can't be done. The African Union is handling it, they say. The African Union is playing a useful role trying to implement the cease-fire agreement, but it has no mandate to protect civilians or reverse ethnic cleansing. Nor does it begin to have the clout of the Security Council.

Pressing too hard on Darfur might upset the peace process in southern Sudan, they say. There, a conflict decades long is waning, with a milestone political agreement signed last week. Growing international attention to Darfur has not upset that process. But Khartoum can hardly be a reliable partner for peace in the south if it is simultaneously murdering civilians and blocking emergency relief in the west.

But where will peacekeepers for Darfur come from? some governments ask. The African Union has offered limited troops to protect cease-fire observers. But commitments in Iraq, Afghanistan and elsewhere in Africa mean that Western militaries are depleted. With slaughter raging in Darfur, the only way to avoid the need for peacekeepers is to send an unequivocal message to Khartoum now.

It is time to move from lip service to conviction. The Security Council should insist, in mandatory language, on pain of targeted sanctions, that ethnic cleansing stop and conditions for the safe return of the displaced be established. Only such clarity stands a chance of being heeded by the killers of Khartoum.

Kenneth Roth is executive director of Human Rights Watch.