Negotiations aimed at resolving Sudan's brutal Darfur conflict faltered before they began on Friday after a leading rebel groups refused to participate. As Nick Wadhams reports from our East Africa bureau in Nairobi, the boycott raises new doubts about prospects for peace in Darfur.

The talks in Arusha, Tanzania are meant to unite Darfur's various rebel factions and were initially seen as a positive and crucial step. They come just days after the U.N. Security Council passed a landmark resolution authorizing the deployment of 26,000 peacekeepers to Darfur.

But the start of the talks was delayed Friday because some rebel groups had not arrived. And already, hopes that the rebels would take advantage of the momentum provided by the resolution seem lost.

About a dozen rebel factions are taking part in the talks, but one important group is absent - the Sudan Liberation Movement, led by Abdelwahid al-Nur. His group argues that it is pointless to talk politics while violence continues.

SLM spokesman Yahia Bolad says al-Nur will not make the same mistake he made in 2006, when he agreed to a peace proposal after months of talks in Abuja, Nigeria, that amounted to nothing.

"The result is that weak Abuja agreement and the government continues killing our people. The humanitarian issue became more worse than ever. For that reason we need to suspend the conflict," he said. "So the matter is not issuing resolutions, the matter is how to implement these resolutions and that's what we're waiting for. When we see U.N. troops on the ground we will start the political process steps."

Al-Nur is one of the Darfur rebellion's founding fathers and a member of Sudan's largest tribe, the Fur. He is popular among many of the 2.5 million people who have been displaced by the Darfur fighting. Some 200,000 people have been killed since the conflict began in 2003.

Without his participation it seems unlikely that the three days of talks in Arusha will result in serious progress. The negotiations are being sponsored by the African Union and the United Nations.

The Sudanese government is not participating in the talks. But foreign ministry spokesman Ali Sadiq Ali says he believes a successful conclusion of the talks in Arusha could lead immediately to new negotiations with the government.

"I don't think it will be a failure," he said. "If they are agreed on a common position I think the next step will be to name the place and the time of the first talks so that the process will start from there on."

The various rebel factions are also calling for the release of the humanitarian coordinator of the Sudan Liberation Army, Suleiman Jammous. The factions believe that Jammous could help jump-start the limited relief work in Darfur and could also help unite the various rebels.

Jammous has been in a U.N. hospital near Darfur for more than a year and the Khartoum government says he will be arrested if he tries to leave.