Previous talks between the government and rebels dragged on for three weeks only to collapse with no agreement, but pressure is mounting on both sides to ease the plight of 1.5 million civilians made destitute by the conflict.
"This time people are more willing to discuss," said Jan Pronk, the UN secretary-general's special representative in Sudan.
Each side accused the other of breaking a ceasefire as talks began after a delay caused by a transport mix-up that left rebel negotiators stranded across the continent for up to four days.
"They are already preparing for war," said Ahmad Muhammad Tugod, chief negotiator for Justice and Equality Movement (JEM), one of two rebel groups present, who accused the government of "systematic bombardment" in the Allaiet area of eastern Darfur.
Government spokesman Ibrahim Muhammad said rebels were the first to attack in Allaiet and troops retaliated, adding that the government was complying with the ceasefire terms.
To complicate matters, two more rebel factions have emerged in Darfur, African Union (AU) and United Nations officials in Abuja said.
Solana said it would be difficult to
mend a break in the ceasefire
European Union foreign policy chief Javier Solana said on Sunday he was increasingly worried by the renewed fighting and said a break in the ceasefire would be difficult to fix.
The EU has promised more than $100 million to fund an extra deployment of 3000 AU ceasefire monitors to Darfur, which AU officials said was now due to begin on Thursday after a delay that contributor Rwanda blamed on poor logistics.
There are currently only 300 AU soldiers in Darfur protecting 150 AU observers monitoring a shaky truce in an area the size of France.
The troops have a mandate to monitor ceasefire violations and protect civilians under imminent threat of attack, according to a copy of the document agreed last week in Ethiopia.
Two rebel groups launched a revolt in western Sudan in early 2003 after years of skirmishes between farmers and nomads over land. They accuse the government of arming militias, known as Janjawid, to crush them and their civilian sympathisers, a charge Khartoum denies.
There are currently only 300
African Union soldiers in Darfur
The UN estimates 70,000 people have died from malnutrition and disease in the past seven months alone.
It is investigating if the campaign of killing, rape and looting by the Janjawid constitutes genocide, as Washington says, and has threatened to impose sanctions on Sudan's oil industry if Khartoum does not stop the violence and disarm the militias.
AU mediators said their first hurdle would be to persuade both sides to sign a humanitarian protocol drawn up at the last round of talks.
The government said it would sign the document, which gives aid workers unrestricted access to the vast region, commits both sides to preventing attacks on civilians and allows for the return of refugees to their homes.
"There was a strong message from the AU and UN to sign the humanitarian protocol and the position of the government is clear - we are definitely going to sign it this time around," said Agriculture Minister Majzub al-Khalifa.
But rebels said they would sign it only after a deal on security issues, which are due to be addressed later on Monday.