Addis Ababa, Ethiopia ? Talks to end the unbridled violence that has killed tens of thousands of people in Sudan’s western Darfur region collapsed Saturday with two rebel groups charging the 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 the government fulfill a list of previous commitments first, walked out Saturday without having met the Sudanese government delegation.

“These talks are now finished,” Ahmed Hussain Adam said on behalf of his Justice and Equality Movement and the Sudanese 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 Africa Union,” Ibrahim said. “It is a delaying tactic … The rebels are not serious.”

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

“This round will not be the last one,” he told reporters in the Sudanese capital, Khartoum.

African Union mediators were working to bring both sides back to the table. “Nobody told us the negotiations have ended,” AU spokesman Adam Thiam said.

The rebels’ main demand was an internationally supervised timeline for Sudan to make good on its promise to disarm shadowy Arab militias accused of killing tens of thousands of black Africans and driving more than a million from their homes in a systematic campaign of terror.

Most of the rebels’ demands were contained in a widely ignored cease-fire deal signed April 8.