Sudan and Darfur rebels will hold fresh peace talks in Libya on 27 October, the Sudanese government and the UN have announced in a joint statement.
The rebel movement in Darfur has fractured over the last year
But the leader of the largest rebel group has told the BBC he will not attend while the conflict continues.
At least 200,000 people have died and some 2m displaced in Darfur since 2003.
Khartoum and pro-government Arab militias are accused of war crimes against the black African population.
Meanwhile, human rights activists have criticised the nomination of an alleged war criminal to a committee to investigate human rights abuses in Darfur.
Ahmed Haroun was the minister responsible for Darfur in 2003 and 2004.
In April, the International Criminal Court issued a warrant for his arrest, accusing him of directing the Arab militias who attacked black African civilians.
"Coming during Ban Ki-moon's visit to Sudan, Haroun's nomination is a stunning affront," said Richard Dicker, from Human Rights Watch.
"It is an insult to the Darfur victims who filed complaints with the vain hope that the government would take them seriously."
The announcement of talks follows a meeting between UN chief Ban Ki-moon and Sudan's President Omar al-Bashir in Sudan's capital, Khartoum.
"The government of Sudan pledges to contribute positively to secure the environment for the negotiations, fulfilling its commitment to a full cessation of hostilities in Darfur and agreed upon ceasefire," the statement said.
It said that the UN "expresses the hope that parties will co-operate fully" with UN and African Union (AU) mediators to ensure the success of the talks in Libya.
Most of about a dozen rebel groups had already agreed to adopt a common negotiating position in talks with the government following a meeting last month in Tanzania, but the Sudan Liberation Movement leader boycotted those talks.
Abdul Wahid el-Nur, based in Paris, told BBC News there was no point in talks until the fighting stops.
"We are not going to Libya to negotiate unless we can guarantee the security of our people. This is a failing process and the SLM is not a movement that fails," he said.
Mr Ban has been pressing hard to get the splintered rebel groups back to the negotiating table.
A peace agreement was signed in 2006. The Sudanese government backed the deal, but only one rebel faction signed up.
In Sudan, Mr Ban also said plans to send a 26,000-strong UN-AU into Darfur next year were "on good track".
A beleaguered AU peacekeeping force now in Darfur has less than 6,000 deployed in the vast region.
'Shocked and humbled'
On Wednesday, the UN chief visited a refugee camp in Darfur.
Ban Ki-Moon was mobbed by Darfur refugees on Wednesday
He was greeted by thousands of people at Al Salaam camp, near El Fasher in North Darfur state, who chanted "Welcome, welcome Ban Ki-Moon".
After the visit to the camp, which holds 48,000 people, Mr Ban said he had wanted to use his position to give the refugees hope.
"I was so shocked and humbled when I visited [the] camps. I was shocked at the poverty and hardship all these tens of thousands of people were undergoing," he said.
The welcome was in stark contrast to his earlier visit to the UN compound in El Fasher, when protesters gathered shouting anti-UN slogans.
Most of the refugees in Darfur are black Africans - although reports suggested those who staged the demo were chanting pro-government slogans in Arabic.
The protests were an illustration of how complicated the Darfur situation is, says the BBC's Laura Trevelyan, who is travelling with Mr Ban.
On Friday, Mr Ban heads to neighbouring Chad, where at least 200,000 Darfur refugees have fled.