"Kingibe expressed disappointment that one week after the intervention of the AMIS to diffuse the tense situation between the Sudan Liberation Movement/Army and Arab nomads in the village of Malam, 50 km north of Nyala [the capital of South Darfur State], the SLM/A remains intransigent," the African Union (AU) said in a statement.
The SLM/A attacked the nomads on 25 August, killing a number of them and abducting seven nomads and 3,100 camels.
Kingibe urged the nomads to continue to resist the temptation of taking the law into their hands, warning it would only lead to the further deterioration of the security situation on the ground. He demanded that the SLA/A immediately release the abducted persons and camels.
"The Special Representative condemns not only the provocative banditry of the SLM/A, but also their continuing refusal to cooperate with the AMIS intermediaries," the statement added.
The AU's condemnation coincided with the conclusion of a three-day round of consultations conducted by AU Special Envoy Salim Ahmed Salim in preparation for the resumption of the Darfur peace talks in the Nigerian capital, Abuja, on 15 September.
In a separate statement on Friday, Salim expressed his satisfaction with the "unequivocal commitment of the Sudanese government" to contribute to the success of the forthcoming round peace talks.
The chairman of the Sudanese government's delegation to the Abuja negotiations, Majdhub al-Khalifah, said in a statement to the official Sudanese news agency, SUNA, that Sudanese President Umar al-Bashir had affirmed his support for peace and stability in the region and hoped the upcoming session of negotiations would be successful.
Observers on the ground in Darfur warned in August that the SLM/A chain of command was disintegrating and that 'warlordism' was on the rise in the region.
While meeting with leaders and field commanders of both the SLM/A and the other main Darfur rebel group, the Justice and Equality Movement (JEM), Salim emphasised the importance of unity within the rebel movements. He appealed to the leaders to foster a spirit of cohesion in their discussions on the various issues that would be considered at the upcoming talks.
The conflict in Darfur, which began in February 2003, pits Sudanese government troops and allied militias like the Janjawid - accused of terrorising the region's non-Arab tribes - against the SLM/A and the JEM, who claim to be fighting the marginalisation of their region by Khartoum.