Talks to end violence in the region of Darfur in western Sudan collapsed on Saturday, with two African rebel groups charging that Sudan's Arab-led government had not kept its end of the bargain.

Mediators worked late into the night trying to save the negotiations, which began Thursday at the African Union headquarters in the Ethiopian capital. But the rebels, insisting that the Sudanese government fulfill a list of earlier commitments first, walked out on Saturday without meeting the government delegation.

"These talks are now finished," Ahmed Hussain Adam said on behalf of his Justice and Equality Movement and the Sudan Liberation Army. "We are leaving Addis Ababa."

Ibrahim Ahmed Ibrahim, spokesman for the government delegation, said Sudan was not prepared to accept preconditions. "The demands of the rebels are not acceptable, and it is a disrespect to the African Union," he said.

Sudanese Foreign Minister Mustafa Osman Ismail said the government remained open to further negotiations.

The rebels' main demand was an internationally supervised timeline for Sudan to make good on its promise to disarm a shadowy Arab militia called the Janjaweed, which is accused of killing tens of thousands of black Africans and driving more than a million more from their homes.

The rebels were also seeking a government commitment to respect previous agreements to allow an international inquiry into the killings, prosecute those responsible, lift restrictions on humanitarian workers and release prisoners of war.

Most of the rebels' demands were contained in a widely ignored cease-fire deal signed with the government on April 8.