African Union ceasefire monitors said they had launched an investigation into the alleged raid, but had so far found no evidence to support the insurgents’ claim.

"As is the case with every other round of talks, the government of Sudan is violating the ceasefire agreement," said Abdulrahman Musa, head of the Sudanese Liberation Movement (SLM) and Sudanese Liberation Army (SLA) delegation to an African Union peace conference in Abuja.

Speaking on the sidelines of a preliminary seminar on power-sharing, Musa told reporters that his group and a second rebel force, the Justice and Equality Movement (JEM), had lodged a complaint with AU ceasefire monitors and conference mediators.

The representative of the AU commission monitoring the Darfur ceasefire, Babagana Kingibe, told reporters that the allegation was being investigated.

"We’ve asked our troops to verify," he said. "They have made a preliminary survey and so far they have not found any evidence of any attack.

"We have asked the SLA to give us the coordinates of the position where this attack is supposed to have taken place. They are going to provide us the coordinates and we shall send a team to investigate whether such an attack indeed took place or not," he said.

Ambassador Kingibe said that the insurgents had warned mediators that the group was "considering" pulling out of the talks but had agreed to wait for the outcome of the inquiry.

Previous rounds of talks on ways to end a 30-month-old conflict which has left some 300,000 dead have been disrupted and in one case all but aborted by accusations that one side or the other had breached the ceasefire.

"During the past week the government of Sudan, through the Janjaweed militia, attacked the positions of the Sudanese Liberation Army. They killed, burned and looted in many areas and also raped many women and young ladies," Musa alleged.

"In the area around the Jabal Mara mountains, 17 were killed in Korbia in north Darfur on September 17 and 13 were killed yesterday in western Jabal Mara. The fighting is continuing in the area," he said.

"In the final analysis this violation will not create a conducive environment to reach a settlement during this round of talks," he said.

Musa heads a delegation of leaders from the SLM and its military wing the SLA, which is thought to be loyal to the movement’s chairman Abdul Wahid Mohammed Nur. A second faction, under SLM general secretary Mani Arko Minawi, has already boycotted the talks.

Both groups claim to represent SLA fighters on the ground.

Last month the rebels were themselves accused by the African Union peacekeepers of breaching the ceasefire with a bandit attack on a camel caravan.

AU mediators have divided the government and rebel delegations in Abuja into groups to debate a series of issues — power sharing, wealth redistribution, security and government organisation — ahead of full political negotiations next weekend.

The launch of the rebel uprising in February 2003 in Darfur prompted a scorched earth campaign by the government, which unleashed Arab militias such as the Janjaweed against minority villages suspected of supporting the rebels.