Commanders from a large Darfur rebel faction have threatened to boycott a unity meeting on Friday seen as crucial to prospects for peace, unless the Sudanese government allows a senior rebel figure to attend.
The latest hitch in the African Union and United Nations sponsored peace process coincided with the first African troop pledges to a new international peacekeeping force, approved by the United Nations this week and given guarded backing by Sudan.
Expected to cost more than $2 billion in the first year, the so-called "hybrid" force will assume authority by Dec 31 over 7,000 AU soldiers who have struggled to stop violence in Darfur.
International experts say 200,000 people have been killed and 2.5 million displaced. Sudan says about 9,000 have died.
Five African nations -- Burkina Faso, Nigeria, Egypt, Cameroon and Ethiopia -- have pledged to send peacekeepers, a top AU official said on Thursday, and South Africa said it would consider adding to its 97 troops already there.
But the task of making up the 26,000-strong force is expected to take many more months.
A faction leader from the Sudan Liberation Army (SLA) told Reuters on Thursday its commanders would not attend Friday's peace talks in Arusha, Tanzania unless the SLA's humanitarian coordinator was allowed to go too.
Suleiman Jamous has been virtually imprisoned in Kordofan, near Darfur, for 13 months after being moved to a U.N. hospital there for treatment. Khartoum says it will arrest him if he leaves.
Observers say Jamous is critical as the rebel liaison with the world's largest humanitarian operation in Darfur, which has been forced to scale down because of attacks on their convoys, leaving some 500,000 out of reach of aid.
They also say he is key to uniting rebel factions and military commanders in Darfur with political leaders outside the region, one of the biggest obstacles to a settlement in Darfur.
This week 11 prominent activists including South African Archbishop Desmond Tutu, former U.S. Ambassador to the United Nations Richard Holbrooke, former Czech President Vaclav Havel, and Nobel Peace Prize Laureate Jody Williams, wrote to President Omar Hassan al-Bashir requesting his release.
"Our commanders on the ground are saying that unless Jamous goes to Arusha, they will not go," one SLA faction head Abdallah Yehia told Reuters.
"I told the U.N. and AU this, but they say it is difficult. I ask why is it difficult? He is in a U.N. hospital," Yehia, from the SLA-Unity group, said. Yehia said he was travelling to Arusha in Tanzania, but that his commanders were refusing to go.
Sudan on Wednesday said it was ready to consider releasing Jamous, but said neither U.N. Darfur envoy Jan Eliasson nor his AU counterpart Salim Ahmed Salim had raised the issue in talks.
U.N. spokesman George Somerwill said it had been raised with the government, who said they would consider his release once actual peace talks began.
A visiting U.N. rights envoy issued a general call on Sudan to curb the powers of its security forces amid continuing rights violations across the country.
Sima Samar, the U.N. special rapporteur on human rights in Sudan, said during a visit to Sudan there were some positive signals from Khartoum but still many problems, including the arrests of political opponents and journalists.
The U.N. and AU will chair the Arusha meeting due to start on Friday with the aim of getting a joint rebel negotiating platform for peace talks.
Mostly non-Arab rebels took up arms in early 2003 accusing central government of neglect. Khartoum mobilised mostly Arab militias, known locally as Janjaweed, to quell the revolt.
After an AU-mediated peace deal last year signed by only one of three rebel negotiating factions, the non-signatories split into more than dozen factions.