Frantic diplomatic efforts were under way today to maintain foreign peacekeepers in Sudan’s war-torn western region of Darfur, as government troops continued a week-long assault on rebel-held villages.

Human rights groups warned that the region was poised to topple into an abyss of rape and genocide if African Union (AU) soldiers leave at the end of the month as scheduled.

The Sudanese Government is blocking the arrival of a United Nations force and today appeared to order the immediate withdrawal of AU soldiers.

Hundreds of thousands of people have already died and millions more made homeless since fighting began in 2003 between rebels and government forces.

James Smith, chief executive of the Aegis Trust, which campaigns against genocide, said that the expulsion of foreign peacekeepers would make it impossible for aid agencies to deliver help to Darfur’s displaced millions.

"By crippling that lifeline, the Government of Sudan is 'deliberately inflicting on the group conditions of life calculated to bring about its physical destruction in whole or in part'. Under the terms of the United Nations Genocide Convention, this constitutes genocide,' he said.

Kofi Annan, UN Secretary-General, called on Khartoum to "reconsider" its position.

Last week the United Nations Security Council passed a resolution to deploy 20,000 troops and police in Darfur. They would replace a cash-strapped force of 7,000 African soldiers which have struggled to protect civilians and aid workers in an area the size of France.

But the plan was rejected by the Sudanese Government which said it would not allow UN troops on its soil. Instead Khartoum is reported to have launched a fresh wave of attacks on villages in North Darfur.

Today Jamal Ibrahim, a Foreign Ministry spokesman, said that the AU had indicated it did not have the resources to stay past the end of the month.

"If they are unable to continue with their assignment in Darfur beyond September 30, then they have to leave before that date," he said.

A second spokesman later clarified the position after hurried meetings with AU officials, saying the African troops could stay if their mandate was renewed.

Khartoum plans to send 10,000 of its own troops to Darfur as part of a peace force instead. The proposal sends shudders through aid workers who point out that Sudanese soldiers have been responsible for some of the worst atrocities.

However, they dare not speak out for fear of being expelled from Darfur. Publicly they say they are committed to maintaining their operations. Privately they say the withdrawal of foreign troops would be the worst possible result.

One aid worker said: "We are very, very concerned about what this means for us and the people who need medicine and food. Darfur is already a difficult and dangerous place for us to work, but without an international force on the ground things will get a lot worse for everyone."

One rebel faction signed a peace agreement with the government in May but the violence has only intensified. Eight aid workers were killed in July making it the bloodiest month since fighting began. David Mozersky of the International Crisis Group said the only hope lay with a renewed AU mandate.

"The AU force is far from ideal, but in the interim we cannot allow there to be a vacuum. That would be a disaster for the population," he said.

Darfur’s rebels took up arms in 2003 against a Government they accused of neglect. Khartoum’s Arab-dominated regime responded with a scorched earth policy. They enlisted the support of the Janjaweed, whose mounted fighters razed villages suspected of harbouring rebels.

More than a quarter of million people have died from the fighting, disease or hunger with some two and a half million crowded into squalid aid camps.

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