The Sudan Liberation Movement on Tuesday called for a delay to African Union sponsored peace talks between Khartoum, the SLM and fellow rebels the Justice and Equality Movement that had been set to resume on August 24.
"Those problems require a political solution which is the only way for resolving the Darfur crisis," Ismail said.
The SLM cited "preparations for our general assembly" as the reason for the delay.
Ismail called upon the African Union to exert pressure on Darfur rebels to ensure their participation in the talks in the Nigerian capital Abuja.
"The government has not yet received from the African Union any suggestion of postponing the negotiations," Ismail said.
Violence broke out in Darfur in February 2003 when a rebel uprising led Khartoum to unleash Arab militias known as the Janjaweed in a scorched-earth campaign.
The conflict has claimed between 180,000 and 300,000 lives, displaced around 2.4 million people and sent more than 200,000 fleeing to neighbouring Chad, sparking one of the world’s worst humanitarian crises.