Observers said splits in the main rebel groups was the main reason for the delay as two leaders of the Sudan Liberation Army (SLA) now claim the presidency of the movement which took up arms in early 2003 accusing the central government of monopolizing power and wealth.
"The 7th round of the Abuja talks ... is now rescheduled to Nov. 28 instead of Nov. 21 for logistical reasons," the AU said in a statement.
Six previous rounds of talks in the Nigerian capital Abuja have made little headway because of rebel squabbles and escalating violence on the ground. U.N. officials have said they are optimistic for a deal by the end of the year.
The U.S. State Department in Washington said Assistant Secretary for African Affairs Jendayi Frazer would head to Darfur on Thursday for talks with rebel leaders this weekend to urge them to overcome their divisions and attend the peace talks in Abuja on common terms.
Canada's special envoy for peace in Sudan, Mobina Jaffer, said she was not optimistic about the talks after a rebel conference elected Minni Arcua Minnawi president to replace the incumbent Abdel Wahed Mohamed el-Nur, a move not recognized by all factions in the group. Nur refused to attend the meeting.
"I'm very worried about the rebel splits," she said during a visit to Darfur. "For the first time I'm pessimistic about Sudan," she said. Jaffer has worked on Sudan for four years.
The AU gave no further details on the delay but said the head of mission in Sudan, Baba Gana Kingibe, would meet with Minnawi, whom they described as a leader of a faction of the SLA.
The State Department said Frazer would be accompanied by Roger Winter, Deputy Secretary Robert Zoellick's special representative for Sudan, and they would work together with Kingibe.
"They will underscore Deputy Secretary Zoellick's message that peace and reconciliation in Darfur can only be achieved through a political settlement at the Abuja peace talks, not by violence," a State Department spokeswoman said.
The United States has called the Darfur violence genocide, a charge Khartoum denies. The International Criminal Court is investigating alleged war crimes in the region. (additional reporting by Caroline Drees in Washington)