Sudan has announced a unilateral ceasefire in Darfur to coincide with talks in Libya to try to end the four-year war.
A Sudanese presidential adviser made the announcement at the start of talks in the city of Sirte.
But two of the main rebel groups have boycotted the talks in a row over invited factions, despite a threat of UN Security Council sanctions.
Some 200,000 people have died and 2m have been displaced in the conflict.
Sudan's President Omar al-Bashir had said last month he was prepared to call a truce for the talks.
At the Sirte gathering, Sudanese presidential adviser Nafie Ali Nafie said: "We announce a ceasefire from this moment, and we will respect it unilaterally."
However, several ceasefires have previously been agreed and none has ended the violence.
The African Union envoy for Darfur opened proceedings by saying the talks were a new opportunity for the region.
"Today marks another milestone in our collective search for peace in Darfur," Salim Ahmed Salim said.
"The journey has been long, arduous and extremely challenging. And the results... have been mixed. But today we are here in this historic city of Sirte for another new beginning."
Fighting in Darfur began in 2003 when rebels attacked government targets.
Sudan's government then launched a military and police campaign in Darfur.
A 2006 peace deal faltered because it was signed by the Sudanese government and only one rebel group.
The latest talks are being hosted by Libyan leader Muammar Gaddafi.
'Trap'
Both the SLA-Unity and the Justice and Equality Movement (Jem) groups decided not to attend after the UN and the AU - who are mediating the talks - invited other rebel groups they claim have little support, said Mohammed Bahr Hamdeen, a senior Jem leader.
"The mediation has fallen in the trap prepared by the government by making the negotiations an arena for every Jack, Tom and Harry," Mr Hamdeen said.
The UN's special envoy for Darfur, Jan Eliasson, continued to hold out some hope for the talks, at which he will be an official mediator.
"This is the first time in a very long time that we have a chance to start to talk about the concerns of the people of Darfur - the right to return to their villages, the need to stop the violence," he said.
When the conflict broke out in 2003, SLA and Jem were the only two rebel movements. Now, there are at least 12.
Demonstrators protested against the talks in Abu Shouk, one of many refugee camps in Darfur, on Friday.
Many Darfuris from different tribes are united in their support for the key rebel leader, Abdul Wahid.
Large numbers are also strongly opposed to the talks and doubt that the negotiations will lead to any concrete improvements on the ground, says the BBC's Amber Henshaw, in Darfur.
They seem to blindly back Abdul Wahid, she adds, even his decision not to attend the peace talks - which means that their voices will not be represented at the discussions.

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