The latest round of peace talks mediated by the African Union (AU) officially began in the Nigerian capital Abuja on Friday following a six-month break.
However, Boubou Niang, the official spokesman of the AU mediation team, said the negotiations failed to get off the ground over the weekend due to the dispute over foreign respresentatives.
Sudan objected to the proposed presence of observers from Eritrea, which is widely seen as sympathetic to the rebel cause.
One of the two rebel groups said meanwhile that it did not want to see officials from Chad sitting at the negotiating table. It accused the government in N'Djamena of taking Khartoum's side in the two-year-old conflict, which has forced nearly two million people to flee their homes.
Majzoub al-Khalifa, the head of the Sudanese government delegation, accused Eritrea of being the main backer for the two rebel movements, the Sudanese Liberation Army (SLA) and the Justice and Equity Movement (JEM).
Both took up arms in February 2003, accusing the government of neglecting and oppressing the people of Darfur, a semi-desert region the size of France.
JEM, meanwhile said the presence of Chadian mediators at the talks was not acceptable. It accused Chad, which is currently hosting 200,000 refugees from Darfur, of being a key ally of the Sudanese government.
Chad hosted several rounds of peace talks between Sudan and the two Darfur rebel movements last year before Nigerian President Olusegun Obasanjo, the current AU chairman, took over as the official mediator in August, but little progress has been achieved since then.
The Abuja talks hit a fresh impasse on Saturday, but African Union (AU) mediators led by former Tanzanian foreign minister Salim Ahmed Salim, finally brought the different sides together briefly on Sunday.
Officials said observers from Eritrea were present as face-to-face peace talks finally got under way on Monday, but officials from Chad had not yet arrived in Abuja to join the negotiations.
Niang, the AU spokesman, said the first item on the agenda was discussion of a draft declaration of principles prepared by mediators and based on positions submitted by the opposing parties during the previous round of peace talks in Abuja in December.
"The idea is to encourage wide consultations that will lead to compromises, consensus and agreements at this round of talks," he told reporters on Monday.
Subsequent negotiations are expected to agree on ethnic, cultural and religious rights as well as an equitable system for distribution of power and national wealth.
These will address the demands of the mainly black-African residents of Darfur, who have long been suspicious of the Arab-dominated government in distant Khartoum.
Despite the weekend hiccups, all sides said on Monday that they remained optimistic that the talks would bring an end to two years of fighting which have already cost an estimated 180,000 lives.
The United Nations has described the situation in Darfur as the world’s worst humanitarian crisis.
The two rebel movements accuse the Sudan government and its ally, the Janjawid militia movement, of slaughtering tens of thousands of black civilians and burning their villages to the ground in a campaign of “scorched earth” attacks.
The AU plans to send 5,300 more peacekeeping troops to Darfur with the help of the western NATO alliance, to help maintain a fragile ceasefire and protect unarmed civilians. There are already 2,370 AU peace monitors on the ground.
Last week, the International Criminal Court launched a formal probe of allegations of war crimes in Darfur.
Human rights groups and the US government have accused the Sudanese government and its Arab militia allies of committing genocide in Darfur, but the United Nations has stopped short of using such strong language.