Ahmad Tugud Lissan of the rebel Justice and Equality Movement (JEM), flanked by officials of the Sudan Liberation Army (SLA), said the two groups had jointly worked out the terms and handed them to the African Union (AU), which held a ceremonial opening of the talks on Thursday at its Ethiopian headquatrters.
"We are not going to engage in political dialogue until the Sudan government fulfills the conditions set by the SLM and JEM, although we will meet the AU officials separately for consultations," Lissan told reporters on Friday.
The other four conditions are bringing criminals who committed genocide or ethnic cleansing to justice, creating unimpeded humanitarian access for delivery of food aid, release of prisoners of war and detainees and agreement on a neutral venue for future talks.
The rebels say Addis Ababa is not a neutral venue because of the Ethiopian government's friendship with Khartoum.
Lissan added that fulfillment of the six conditions would mean the government had honoured the pledges it made to UN Secretary-General Kofi Annan and US Secretary of State Colin Powell on visits they made to Sudan in late June and early July.
The talks, due to get under way at about 1300 GMT on Friday, are meant to cover the status of a shaky ceasefire in the remote western region, disarmamant of combatants, the humanitarian situation and deployment of AU ceasefire monitors, AU officials say.
"We are not going to engage in political dialogue until the Sudan government fulfills the conditions..."
Ahmad Tugud Lissan,
Justice and Equality Movement
The United Nations says the fighting has displaced more than one million people, triggering one of the world's worst humanitarian crises. As many as 30,000 people have been killed.
The situation has gained increased urgency with the rainy season already affecting parts of Darfur. Aid workers have said the rain, in addition to continued security concerns, will severely hamper desperately needed humanitarian operations.
But Darfur peace efforts remain difficult, despite pressure from the 53-nation AU, the United Nations and the United States.
The Addis Ababa negotiations are chaired by the AU, the United Nations and Chad, with the United States and European Union attending as observers.