A Senegalese spokesman for the AU mediators, Boubou Niang, said on Monday that the meeting was agreed to by all parties at the last minute.
"The session was attended by all the parties, facilitators, partners and observers" in the effort to end two years of civil war in the western Sudanese region, he said.
Earlier, Sudanese Foreign Minister Mustafa Osman Ismail was reported as warning that his government was ready to walk out of the talks if AU mediators allowed Eritrea to take part.
"Any role for Eritrea as a mediator in Abuja is unacceptable and is rejected because neither is the country neutral, nor is it a neighbour of Darfur (unlike Chad, Libya and Egypt or an active AU member such as Nigeria, South Africa and some other countries are," Ismail was quoted as saying.
He had also said AU had been warned that "if the Eritrean delegation went into the meeting hall, the government delegation would not enter".
Talking to Aljazeera on Monday, Osman clarified that Sudan does not object to Eritrea's presence in the Abuja talks on Darfur as long as the country's role does not develop into that of a mediator.
"We have no problem with Eritrea's presence, but we don't recognise it as a mediator. AU should not recognise it as a mediator either," he said.
Hundreds of thousands of people
have been displaced by the war
"As a result of the plan we have presented with regard to the continuation of negotiations, the talks resumed on Monday. AU has distributed a draft of what we may call "the principles of a political solution".
Osman said: "Both sides have received copies of the draft. When they return on Tuesday evening, each side will present its observations on the proposals."
He added: "We can say that by virtue of this plan, we have overcome the question of Eritrea's participation."
Eritrea has long provided refuge to Sudanese opposition groups but denies accusations from Khartoum of arming their military wings. It also accuses Khartoum of supporting Eritrean rebel groups.
The Darfur rebels oppose participation in the Abuja talks by Chad, accusing it of siding with Khartoum.
The fighting in Darfur in western Sudan between rebels and government forces backed by nomadic militias has continued despite a ceasefire last year.
International pressure has intensified to end bloodshed that has claimed hundreds of thousands of lives and led to one of the world's worst humanitarian crises.
The war has claimed 180,000 to 300,000 lives, displaced 2.4 million people and sent another 200,000 fleeing to Chad.
"We have no problem with Eritrea's presence, but we don't recognise it as a mediator. AU should not recognise it as a mediator either"
Mustafa Osman Ismail,
Sudanese Foreign Minister
Violence broke out in Darfur in February 2003 when a rebel uprising against the government led Khartoum to arm nomadic militias known as Janjawid in a scorched-earth campaign.
Humanitarian officials say Darfur is growing more desperate, with not enough funding to meet chaos triggered by drought, famine and the long-term effects of conflict.
Sunday's session was the first face-to-face encounter by parties at the fifth round of Darfur talks, which resumed in the Nigerian capital on Friday after a six-month suspension.
The last round foundered in December as each side traded accusations of truce violations.
There were few immediate details about Sunday's meeting, which the spokesman said lasted 40 minutes and followed separate, closed-door discussions.
The chief AU mediator, former Tanzanian foreign minister Salim Ahmed Salim, "outlined the agenda, methods of work, the code of conduct to be abided by all parties", said Niang.
AU mediator Salim (L) urged all
sides not to play up differences
Participants said he had urged all sides not to say too much to the media to avoid fanning differences and jeopardising the talks.
"Dr Salim stated that the declaration of principle (adopted in December) will be the first item on the agenda ... before taking thematic issues such as, among others, power sharing, wealth sharing and security arrangements," the spokesman said, adding the parties had adjourned and would resume work on Monday.
No deadlines have been set, but the AU wants this to be the final round and to reach a political agreement.