He said the AU was also expecting a final submission of the contribution of the Sudan Liberation Movement (SLM), one of the two rebel groups fighting the Khartoum government, to a revised Declaration of Principle (DoP) before convening a formal meeting of the warring parties to discuss the key document.
"The SLM negotiators are right now working on the document. They have promised to submit it in the course of the day. We are waiting for them," he said.
The presence of Chad has stalled the AU-mediated talks which opened here on June 10 because of the strong opposition of the SLM and the Justice and Equality Movement (JEM) to Ndjamena's role as co-mediator, on the grounds that it is biased against them.
"Nothing has changed except that informal negotiations to get the talks back on track are still going on. Formal talks are yet to resume because of the row over Chad," Mezni told AFP.
He said there was nothing unusual about the hitches.
"In negotiations, you can move forward by two steps and move backward by one step," he said.
"If you recall, the issue came up at the last round of the talks in December and it was resolved. We are also going to thrash this one out. So there is no cause for alarm," Mezni said.
JEM negotiator Mohammed Tugod told AFP his group might meet Nigerian President Olusegun Obasanjo, the current AU chairman, Saturday over the issue.
"It is very likely we will meet Obasanjo to restate our position on Chad. We don't want Chad to participate in any capacity at all," he said.
Chad has an eastern border with Darfur and hosts some 200,000 of the 2.4 million people estimated to have been displaced by the conflict.
Fighting in Darfur broke out in February 2003 when an uprising representing the mainly black population of the region led Khartoum to unleash Arab militias known as Janjaweed, who have been accused of "ethnic cleansing", torture, rape and intimidation.
International pressure has increased to end the war that has claimed between 180,000 and 300,000 lives and displaced some 2.4 million people, especially since the resolution last year of a separate conflict which had engulfed oil-rich south Sudan for more than two decades.
The pressure intensified Saturday when Khartoum and Sudan's largest opposition bloc, the National Democratic Alliance (NDA), signed a landmark reconciliation agreement in Cairo that officials said would boost efforts to bring peace back to Africa's largest country.
The AU's special envoy on the Darfur peace talks, Tanzanian-born Salim Ahmed Salim, foreign partners, facilitators and observers were working hard to break the deadlock, Mezni said.
"We will soon get over it," he added.
African mediators and foreign partners had produced a draft Declaration of Principle to be adopted by the warring parties late Thursday but no progress could be made because of the row over Chad.
Mezni told AFP more SLM delegates arrived Friday for the talks.
"We hope the SLM will now make its final presentation on the DoP since its delegation has been boosted with the arrival of more negotiators," he said.
The AU-mediated talks resumed after a six-month break over mutual accusations of ceasefire violations. The parties have yet to get together outside initial plenary sessions.
The peace talks which began last August in the Nigerian capital have stalled several times because of mutual suspicion and disagreements over some issues.