The peace talks - resumed on Friday - has brought the Sudanese government together again with two rebel groups, the Sudan Liberation Movement (SLM) and the Justice and Equality Movement (JEM).
The heads of the two rebel groups - Muhammad al-Nur and Ibrahim Khalil respectively - were attending for the first time, while Agriculture Minister Majzoub al-Khalifa headed the government side.
AU commission head Alpha Oumar Konare opened the latest round of talks.
Konare, who had informal discussions beforehand with representatives of the Sudan government and the two rebel groups, said he hoped that "this phase of talks will be the last one".
AU officials said on Saturday that Sudanese armed forces arrested but later released three members of a Darfur rebel group on Friday who were trying to contact African Union forces to request help.
Three members of the rebel Justice and Equality Movement (JEM) travelled to the AU headquarters in al-Fashir to seek help after their last main base in Darfur came under attack by the biggest Darfur rebel group in recent days.
"All the parties must refrain from violence that could put in danger the lives of innocent civilians and abide by the agreements already entered into"
Nigerian President and African Union chairman
"The reports I had were that three members of JEM in al-Fashir were arrested," political affairs officer, Jean Baptiste Natama, said.
"We had to intervene to get them released," he said, adding they were released a few hours later.
AU special envoy to Sudan, Salim Ahmad Salim, hailed the delegates for their attendance, urging them to reach a consensus on issues before the talks.
"It is my hope that this session will be constructive. The decision on the part of the Sudanese parties in the conflicts to dialogue should be commended because it signals their determination to move the process forward," he said.
The Abuja peace talks which began in August 2004 were suspended in December to allow for more consultations among the parties who were accusing each other of violating the ceasefire agreements.