Leading article: The protests continue over Darfur, but still the vicious conflict drags on

Some 10,000 hourglasses filled with fake blood will be turned over at noon tomorrow by campaigners in 25 different countries - from Mongolia to Iceland, the United States to the Ukraine - to mark the fourth anniversary of the Darfur conflict and to demand action to end what is by far the world's biggest humanitarian crisis. Meanwhile, the Red Cross has launched another appeal to help people struggling to survive in refugee camps in a region where 90 per cent of villages have been razed.

We have heard all this before. The protests and the appeals continue, but on the ground nothing seems to change, except for the worse. Nearly three million people in Darfur now depend on international food aid - and half a million people are cut off by the fighting from any help at all. Christian Aid is appealing for more money to move the same amount of food as before, only now by helicopter.

Related articles

• Blair sanctions threat on Darfur

The wheels of international diplomacy turn exceeding slow. This week the new UN Secretary-General Ban Ki-moon announced that he and Sudan's president, Omar al-Bashir, have agreed on the need for a quick decision to deploy a new UN-African Union "hybrid" peacekeeping force in Darfur. But this signifies almost nothing. Sudan's ruthless president has a history of making agreements and then reneging on them - as with the 30,000 troops the UN wants to send in to bring peace to the huge faction-torn region.

Campaigners call for tough action against him. The American, British, French and Germany governments have been trying to tighten the screw. But progress is being hampered by Sudan's great ally in the UN Security Council, China, which sells huge quantities of arms to Sudan and in return gets sizeable amount of Sudanese oil. China is responding to behind-the-scenes pressure from the West. It recently told Bashir that it was giving him a "final warning" on Darfur. But diplomats sense that China will still veto any Security Council move for sanctions on Sudan. China insists that a face-saving escape route must be left for Bashir.

The challenge for the West is to come up with that, but in a way which does not allow compromise on the self-evident bottom line of what cannot be allowed in Darfur. Bashir will doubtless offer some last-minute compromise, on deploying the hybrid force. That will not be enough. There is clear evidence in just the past few days that the Sudanese military is still bombing in Darfur - in violation of UN Chapter Seven resolutions, of the Addis peace agreement and of President Bashir's previous promises. It is moving arms into Darfur without notification, contravening earlier commitments. It has broken the ceasefire agreement Bashir agreed to only in January. A compromise from Bashir on the hybrid force is insufficient; there must be adherence to his promises on air attacks and on the movement of arms into the region; and he must honour his commitment to facilitate humanitarian assistance to Darfur.

President Bashir, we know from the past, makes concessions only under pressure. If UN sanctions cannot be agreed upon, then unilateral sanctions should be enforced. Individual businesses such as Rolls-Royce and Siemens, spurred by pressure from activists, have already taken the lead on this, withdrawing from operations in Sudan. On Monday, the governing body of the London School of Economics will be presented with proposals for the university to divest. Other Western institutions should follow, and so should Western governments. The regime in Khartoum must realise, when the world sees the TV footage of those hourglasses tomorrow, that time is not just running out for the people of Darfur, it is running out for Omar al-Bashir too.