Sudanese government representatives and rebels from the western Darfur region have held a brief face-to-face meeting during slow-moving talks in Nigeria.
More than two million people have fled their homes in Darfur
The meeting finally took place after the talks were put off on Saturday, but differences remain on how to proceed.
Disagreements include the question of which countries should assist in the mediation process, and over the agenda.
African Union mediators said talks would continue on Monday, starting with talks on a declaration of principle.
However, Sudanese Foreign Minister Osman Ismail has warned that his government will walk out of the talks in Abuja if the AU allows Eritrea to take part.
"Any role for Eritrea as a mediator in Abuja is unacceptable and is rejected because it is not neutral, nor is it a neighbour to Darfur like Chad, Libya and Egypt or an active African Union member like Nigeria, South Africa and some other countries," Mr Ismail told reporters.
The Darfur rebels have objected to Chad being involved.
Sudan accuses Eritrea of helping rebels in Darfur, while rebel leaders say Chad sides with the Khartoum government.
The UN has said Darfur is one of the world's worst humanitarian crises.
Two years of fighting between rebels and Arab militias have left at least 180,000 people dead and forced more than two million to flee their homes.
As well as the AU, observers from the UN, the EU and other countries are observing the talks in Abuja.
The talks began last August but were adjourned in December.
The government denies accusations that it has backed the Arab Janjaweed militias, which are accused of the worst atrocities such as mass rape, killings and looting.
Some 2,000 AU peacekeepers are trying to monitor a shaky truce.
Nato has agreed plans to airlift more AU troops to Darfur in the alliance's first mission in Africa.
The AU has agreed to increase its force to more than 7,700, but even this number is seen as being too small to cover an area the size of France.