"Internal division will make peace more difficult to attain," AU spokesman Nureddin Mezni said after the pan-African body's special envoy Salim Ahmed Salim met with Darfur rebel leaders in Sudan.
"They need to coordinate their positions," Mezni said.
A fresh round of talks between Darfur rebels and the Sudanese government is due to kick off in the Nigerian capital on September 15 in a bid to end their 30-month-old civil war.
Salim met with leaders from the Sudan Liberation Movement (SLM) - the main Darfur rebel group - and the smaller Justice and Equality Movement (JEM).
"The SLM leaders declared their commitment to the peace process and their acknowledgement of the role being played by the AU troops in Darfur," Mezni said, in reference to 6,000 peacekeepers on the ground.
Salim was due to hold talks with Sudanese President Omar al-Beshir. Khartoum has vowed to do its utmost to ensure that the next Abuja round would yield a final agreement on Darfur.
According to some estimates, up to 300,000 have died and more than two million been displaced as a result of the war pitting government troops and militias against rebels in the western Sudanese region.
Although the humanitarian situation has improved and the violence receded in recent months, incidents continue to plague peace initiatives and efforts to repatriate the displaced.
The UN mission in Sudan quoted a government report alleging that five troops had been killed in an ambush earlier this week in Darfur.