There is a weary inevitability about reports that the Sudanese government's Janjaweed militia has crossed the border into eastern Chad to attack refugees who had fled there from the fighting in Darfur. The detail is grimly familiar too: homes burned, an imam killed, a woman set alight, a man disembowelled. Armed groups from both Chad and Darfur regularly cross the border at will. Large numbers of people are on the move.

Darfur, where already 200,000 people have died and 2 million have been made homeless, is now seeing an influx of displaced people. Some 1,000 refugees have just arrived in Um Dukhun in West Darfur, fleeing increasing violence in Chad and in the Central African Republic. It is a strategy of desperation, for in Darfur the rebel groups have splintered and are fighting one another as well as the Sudanese army. There is no front line, only a cauldron of escalating violence and banditry with all parties persistently violating ceasefire provisions. More guns than ever are to be found in the refugee camps.

The region where the borders of Sudan, Chad and the Central African Republic meet is dissolving into sporadic and bloody anarchy. Governments trade accusations that each is supporting the other's rebels. In the face of all that, more than 100 aid workers have left Darfur in the latest evacuation of relief workers from the lawless region.

What is to be done? The French have tried to intervene with attacks by Mirage F1 jets on anti-government rebels in the north-east of the Central African Republic. The aim, Paris says, is to stabilise a region which is in danger of "Somalisation". But reports from the ground say the operation has had a devastating impact on civilians.

Khartoum is callously disregarding the situation. Sudan persists in its opposition to the United Nations' plan to send 20,000 peacekeepers to Darfur. It insists that the most it will tolerate is a slight strengthening of the weak African Union force whose 7,000 ill-equipped soldiers have proved ineffectual in the province.

The international community must do two things. First it must continue to pour humanitarian aid into Darfur where the need is dire. The EU this week announced a further €17m in aid. That is good, though it will not stop the Sudanese authorities and rebel movements deliberately targeting relief operations. More is needed. The time has come for the 20,000 UN peacekeepers to be deployed - in eastern Chad. Their presence there will bring some stability to the area. And it will send a warning that the world is ready, on Sudan's doorstep, to cross the border if Khartoum allows the situation to deteriorate further.