The Archbishop of Cape Town and Nobel Peace Prize winner Desmond Tutu has called for sanctions to be imposed on Sudan if it fails to accept a UN peacekeeping force.
"The world can't keep saying 'Never again'," the archbishop told the BBC.
Archbishop Tutu's comments come as the UN's humanitarian aid chief Jan Egeland warned that Darfur, in western Sudan, was in "free fall".
He said world powers must insist on deploying UN peacekeepers there to avert a complete collapse, adding that without a UN peacekeeping force there, most if not all foreign aid organisations are likely to pull out of Darfur, leaving its already devastated civilian population further exposed and at risk.
In his interview with BBC Five Live, Archbishop Tutu continued, "We have a horrendous tragedy unfolding in Darfur".
He added that the UN should give Sudan a deadline and say to the government, "If you do not agree to a peacekeeping force, you will have to face sanctions."
Campaigners in cities around the world, including New York, London, Abuja, Nairobi, Paris, Berlin and Kigali, are preparing to host major demonstrations in support of the proposed UN peacekeeping force for Darfur.
The demonstrations, part of the worldwide initiative Global Day for Darfur this Sunday, will also urge Sudan to accept the resolution passed on Darfur, which backs the creation of a UN force but states that it can only be deployed with the approval of the Sudanese government.
Archbishop Tutu accused the international community for having less urgency to respond to crises in Africa than in other parts of the world.
"The harsh truth is that some lives are slightly more important than others... If you are swarthy, of a darker hue, almost always you are going to end up at the bottom of the pile."
Meanwhile, Oscar-winning US actor and director George Clooney joined Nobel Peace Prize laureate Elie Wiesel in addressing the UN Security Council on Thursday on the humanitarian crisis in the Darfur region.
The two celebrities appealed for world action to protect the people of Darfur. "We need the international community to commit all of its resources to bring an end to this extraordinary suffering. The critical hour for Darfur is now," said Clooney.
