Sheikh Hamad bin Jassem Al-Thani, the Qatari prime minister, announced on Monday that Jem and the Khartoum government had agreed to a series of confidence-building measures following a week of peace talks in Doha, the capital of Qatar.
The accord followed a long meeting between the heads of the two delegations, Khalil Ibrahim, the Jem chief, and Nafie Ali Nafie, an aide to Omar al-Bashir, the Sudanese president.
But other rebel factions are refusing to talk to Khartoum and Al Jazeera has learned there are serious disagreements between anti-government groups about the Doha accord.
The US also gave the announcement a cautious welcome, saying it would not change Washington's opposition to postponing any indictment of the Sudanese president by the International Criminal Court (ICC).
ICC judges are expected to rule within weeks on whether to issue an international warrant for his arrest on grounds of alleged war crimes in the western Sudanese Darfur region.
Abdalmahmoud Abdalhaleem, the Sudanese ambassador, called Tuesday "a great day for the people of Sudan" as the "landmark agreement" would lead to the end of the conflict "once and for all".
According to the UN, 300,000 people have died and more than 2.2 million have fled their homes since rebels in Darfur rose up against the Khartoum government in February 2003.
The Sudanese government disputes the figures, putting the death toll at 10,000.