Leaders of more than 10 Darfur rebel groups have held talks in Tanzania in search of a common position for peace talks with the Sudanese government.
Splits among the rebels have hampered previous peace talks
The UN and African Union say the three-day meeting is vital in the wake of a UN resolution approving the deployment of peacekeepers in Darfur.
The UN envoy to Sudan, Jan Eliasson, told delegates they had the power to make a positive change in the region.
But expectations were weakened by the absence of one prominent rebel leader.
Earlier, UN Secretary General Ban Ki-moon called the coming weeks and months "a crucial period in the quest for peace in Darfur".
In a report to the UN Security Council, Mr Ban said that "as long as hostilities continue in Darfur, efforts to reach a political settlement and achieve durable peace will not succeed".
The BBC's Kevin Mwachiro in Arusha says the mood at the meeting improved considerably during its first full day on Saturday.
Representatives from all the invited groups attended the discussions, except those from the SLM faction led by Abdul Wahid Mohammad Ahmed al-Nur.
A programme is running and the leading figures from each faction are talking, our correspondent says.
Pekka Haavisto, the senior adviser to the UN special envoy to Darfur, said the conference was already a success simply because it had brought the various factions together.
"These are people who have not been talking with each other for a long time," he said.
The Egyptian mediator, Ahmed Abdul Zayed, said it was vital that the rebel groups iron out their differences.
"It is not seen as logical to have the government of Sudan negotiating with 10 or 15 difference factions, so we have encouraged all the participants at the Arusha meeting to... find a minimum common denominator among themselves," he said.
But expectations of a successful outcome for the conference have been weakened by the refusal of Abdul Wahid Mohammad Ahmed al-Nur to attend.
He told the BBC he had no intention of going to Arusha because he wanted the killing in Darfur to stop before he would participate in negotiations.
KEY REBEL PLAYERS
SLM: Minni Minnawi's faction signed 2006 peace deal
SLM: Abdul Wahid Mohammad Ahmed al-Nur's faction rejected peace deal
Jem: Khalil Ibrahim, one of the first rebel groups, rejected deal
Rebel negotiator: Suleiman Jamous
SLM Unity: Abdallah Yehia
UFLD: recently formed umbrella group including SLM commanders
Other breakaway SLM commanders: Mahjoub Hussein, Jar el-Neby and Suleiman Marajan
Estimated to be more than 13 rebel factions in Darfur
Mr Nur added that, in his view, the rival rebel leaders would emerge from the talks with nothing but a piece of paper.
The BBC's David Bamford says Mr Nur is regarded as the founding father of the Darfur rebellion against Khartoum's rule, and as such his involvement in any peace process seems vital.
His absence from the Arusha talks will be felt, our correspondent says, as splits between the rebel groups were seen as a key factor in the failure of previous talks with the government to end the four-year war.
At least 200,000 people are believed to have died and more than two million have been left homeless since 2003.
Sudan's government and pro-government Arab Janjaweed militias are accused of war crimes against the region's black African population, although the UN has stopped short of calling it genocide.
The talks follow Tuesday's UN Security Council resolution to send 26,000 peacekeepers to Darfur.
Though the fighters in Arusha have welcomed the announcement that more peacekeepers will be deployed, they know that a political solution is the only way forward, our correspondent says.
After months of wrangling, Sudan agreed to the UN resolution after it was watered down.