Jem rebels are involved in negotiations with the government
The government of Sudan has signed a ceasefire agreement with one of the main rebel factions in Darfur.
The deal with the Justice and Equality Movement (Jem) includes a framework for further talks, and the cancellation of death sentences for 100 fighters.
It is being seen as an important step towards peace, though the other main rebel group has refused to enter talks.
The seven-year war between forces loyal to the government and rebels in Darfur has lost intensity in recent years.
But the UN estimates 300,000 died in the worst years of the conflict. Some 2.5 million people are still displaced.
'Heal the war'
The agreement reached on Saturday in the Chadian capital N'Djamena, according to a Jem spokesman and an aid to Sudanese President Omar al-Bashir, starts with an immediate ceasefire, but is not a permanent peace accord.
James Copnall, BBC News, Khartoum
The Justice and Equality Movement is perhaps the strongest of the Darfur rebel groups.
Two years ago they shocked Sudan by attacking Omdurman, across the Nile from the capital Khartoum. Jem has not looked like matching that feat since, but the ceasefire between it and the government can only help improve stability in Darfur.
The framework agreement, which lays out the issues for talks, is also welcome in its detail. It is clearly a consequence of the rapprochement between Chad and Sudan.
Chadian President Idriss Deby is widely believed to have supported Jem, perhaps in part because Jem's fighters are from his Zaghawa ethnic group. Last month President Deby visited Khartoum, and both sides agreed to stop supporting each other's rebels.
But no peace agreement can be conclusive without the Sudan Liberation Army-AbdulWahid faction. At the moment this other strong rebel group is refusing to talk with the government.
It includes a framework for further talks, during which issues such as the sharing of power and wealth, and the return of internally displaced people and refugees will be discussed, possibly this week.
Mr Bashir said he would cancel death sentences handed out to Jem prisoners and free 30% of those he had pardoned immediately.
More than 100 men were sentenced to death by hanging after being found guilty of taking part in a Jem attack on Omdurman in May 2008, in which the government said more than 200 people were killed.
"Today, we signed an agreement between the government and Jem in N'Djamena, and in N'Djamena we heal the war in Darfur," the president said in a speech broadcast on state television.
Jem spokesman Ahmed Hussein said the deal would be formally signed in Qatar's capital, Doha, on Tuesday.
"It's a significant step for peace in Darfur," he told the Associated Press. "It is a considerable achievement for both parties."
The BBC's James Copnall in Khartoum says the Jem is the most significant of the many rebel groups taking part in peace talks in Qatar, which aim to reach a final agreement by 15 March.
The Sudanese official in charge of the Darfur peace process, Ghazi Saleh al-Din, said other groups could also be included.
"It does not exclude other movements," he said. "I think we can try to emulate the agreement which we signed with Jem and try to speed up the process so that we can try to a final agreement as soon as possible."
When conflict broke out in Darfur early in 2003, there were just two major rebel groups - the Jem and the Sudan Liberation Army (SLA).
The insurgents later splintered into an array of competing factions.
The Jem has been the most significant fighting force in Darfur, armed with weapons that Sudan says come from neighbouring Chad.