The Janjawid, made up mainly from the nomadic Arab tribes from the area, have been accused of much of the killing in Darfur over the past four years.
The AU's comments substantiate an earlier UN reports that said hundreds of Janjawid fighters were gathering in the area close to el-Geneina.
On Monday, a report by the UN Mission in Sudan said "armed militia have been mobilising in large numbers over the last five days in the general area of Abou Souroug and Sliea [approximately 50km north of el-Geneina].
"The reason behind the massive militia mobilisation is so far not known".
Burning and pillaging
Janjawid forces have also been reported active north of ed-Daein, a town about 450km southeast of el-Geneina, where there were reports a Janjawid force, separate from those near el-Geneina, has been attacking villages far to the east of the Darfur region for the past two days.
A spokesman for the Sudan Liberation Movement (SLM), the only armed group to sign a May peace accord with the government, said the Janjawid had pillaged food and burned houses in an attack which began on Monday and continued on Tuesday.
"We want to affirm that government officials who say the situation is stable in Darfur ... want to deceive the Sudanese people"
Six civilians have been killed in the attacks, he said.
Al-Tayyib Khamis, an SLM spokesman, said the fighters were using heavy weaponry given to them by the government, and the attacks were a "blatant violation" of the Darfur peace agreement.
Khamis said: "Nine months after [the signing of the peace agreement], Darfur has not lived with stability. We want to affirm that government officials who say the situation is stable in Darfur ... want to deceive the Sudanese people."
Rights group and Western governments say the Sudanese government has used the Janjawid as a military force to attack those who oppose it as well as sanctioning attacks on civilians.
The government denies this and says the Janjawid are outlaws.
Ravaged by violence
Darfur has been ravaged by violence since 2003, when rebels took up arms, accusing the government in Khartoum of ignoring the region.
Experts estimate 2.5 million people have been driven from their homes in four years of conflict in Darfur.
Omar Hassan al-Bashir, the Sudanese president, has refused to allow the deployment of thousands of UN peacekeepers to support the 7,000-strong AU mission in Darfur.
Al-Bashir said the AU force was strong enough and that instead the UN could give money and logistical help to a hybrid force.