The UN Secretary-General's Special Representative to Sudan, Jan Pronk, said a Ugandan insurgent group, the Lord's Resistance Army (LRA), was to blame for much of the violence in southern Sudan. The group had hindered demining work and the opening of roads in the area, he added.

"The Comprehensive Peace Agreement, North-South, is on track," Pronk told reporters, after urging the UN Security Council to renew the mandate of the UN Mission in Sudan (UNMIS) and expedite its deployment.

The peace agreement signed in January between Khartoum and a former southern rebel movement, the southern Sudan People's Liberation Movement/Army (SPLM/A) could present an opportunity to deal with the LRA militarily, Pronk said. However, he added, a diplomatic solution might also be necessary because the group seemed to have the ability to regenerate.

Pronk said peace talks aimed at ending the conflict in Darfur between the government and rebels were under way in the Nigerian capital, Abuja.

He said it was hard to pin down the causes of increasing violence in Darfur, but to "a certain extent" it was related to disputes between nomadic communities and farmers, and a split within the region's main rebel group, the Sudan Liberation Movement/Army (SLM/A).

"There are groups that are not government and that are not SLM, but the result of splits and splits and splits," he added.

Pronk said he had urged the Security Council to issue an ultimatum to the parties to the conflict in Darfur to come to a comprehensive peace agreement by 31 December.

"There is no reason any more to solve the problem through further shooting and fighting. We don't accept it any more," he said, noting that a similar ultimatum had led to progress when the southern peace agreement was being negotiated.

Pronk said the riots in Khartoum following the death of SPLM/A leader John Garang, in a July helicopter crash, had exacerbated ethnic tensions.

The establishment of essential political institutions and legal reforms in line with the southern peace pact had been slow, he said.

New tensions in eastern Sudan and the fact that certain areas of the south had been left as ambiguous zones of "special status" in the peace agreement were other causes for concern, he added.