The United Nations and African Union mediators at the Darfur peace conference in Libya insisted Sunday the peace process will continue despite the absence of key Darfur rebel groups.

U.N. envoy Jan Eliasson said Sudanese government officials and Darfur rebels present at the talks will meet privately Monday in an effort to bring four years of violence in the region to an end.

The peace conference officially opened in the town of Sirte on Saturday, with the Sudanese government announcing a unilateral and immediate cease-fire in Darfur. But the absence of key Darfur rebel groups cast doubt on whether the talks can be successful.

In London, British Prime Minister Gordon Brown praised Khartoum for its cease-fire pledge but warned of more sanctions if progress is not made in Libya.

The United Nations is hoping to achieve a political settlement before the planned deployment to Darfur of a joint 26,000 U.N.-AU peacekeeping force by early 2008.

The fighting in the region between rebels, militias and the government has killed an estimated 200,000 people and displaced more than two million others.

Rebel groups missing from the talks include the Sudan Liberation Army, the SLA-Unity faction, and the Justice and Equality Movement.

A Justice and Equality Movement leader, Ahmed Tugod Lissan, said his group is boycotting the talks because of the presence of minor rebel factions favored by Khartoum.

Some information for this report was provided by AFP, AP and Reuters.