Sudanese rebel groups insisted Friday the government fulfill a list of previous commitments before beginning new peace talks to end fighting in Sudan's western Darfur (search) region, deemed the world's worst humanitarian crisis.

Experts said the negotiations were doomed to fail without concerted diplomatic and military pressure.

Chief among the rebels' demands was a timeline for Sudan to make good on its promise to disarm the shadowy Arab militias accused of killing tens of thousands of black Africans and driving more than 1 million from their homes in a campaign of ethnic cleansing.

The rebels also sought commitments by the government to release prisoners and to lift restrictions on humanitarian aid in the region. Both conditions are part of a widely ignored cease-fire signed April 8.

Analysts said it now was up to world leaders to maintain pressure on Sudan to drive the process forward.

"As the rebels rightly pointed out, you can't have meaningful progress without respect of the myriad of agreements that have already taken place," said John Prendergast, an African specialist at the International Crisis Group (search), a Brussels, Belgium-based think tank.

The Janjaweed, the shadowy Arab militia blamed for much of the bloodshed, did not attend the talks in Addis Ababa, the Ethiopian capital.

U.N. officials, rebels and refugees have accused Sudan's government of backing the Janjaweed with airplanes, helicopter gunships and vehicles. The government denies any involvement in the attacks.

"I don't know what constructive role (the militias) could play at the peace negotiations," said Eric Reeves, a Smith College professor and leading academic expert on Sudan. "You cannot have genocidaires sitting at the peace table."

The U.N. health agency said Friday in Geneva that the killings in Darfur had subsided somewhat during the last six months. Still, the African Union (search), which is sponsoring the peace talks, pledged last week to send 300 troops to Darfur to help protect international observers investigating cease-fire violations.

The World Health Organization estimated the death rate in Darfur is 20 times the norm for a developing country. It said 350 people would die every day in refugee camps during the rainy season unless conditions improved.

Dr. David Nabarro, head of the WHO, estimated that 50,000 refugees from Darfur have died in camps from disease during the last six months. Separately, the U.N. estimates 30,000 people have died in fighting.

The recent peace initiative follows a concerted diplomatic push by U.N. Secretary-General Kofi Annan and Secretary of State Colin Powell, who visited the region earlier this month.

Powell said Friday he expects to hear from U.S. experts next week on whether Sudan officials should be charged with genocide.

Powell said on PBS' "Charlie Rose" show that the U.S. officials were both in western Sudan's Darfur region and on the Chad side of the border talking to displaced people and refugees. But, Powell said, "Too many people are spending too much time arguing about whether it's genocide or not. That's not the issue."

He said the issue is to make sure a humanitarian pipeline was getting to people in need.

Powell said the Bush administration will continue to pressure the government in Khartoum and was discussing with the U.N. Security Council whether the United Nations could act against Sudan.

The peace talks began Thursday, though the two sides had yet to meet face-to-face or agree on an agenda Friday, African Union spokesman Desmond Orjiako said. Chad, which borders Sudan and is hosting more than 200,000 Darfur refugees, also is mediating.

Nomadic Arab tribes have long been in conflict with their African farming neighbors over Darfur's dwindling water and usable land. Violence exploded in February 2003 when two African rebel groups took up arms over what they regard as unjust treatment by the government.

The situation has worsened since then, with the Janjaweed burning villages and killing thousands of people.

Sudan signed a U.N. agreement July 3 calling for disarming the Janjaweed, deploying soldiers, facilitating aid and allowing international troops and monitors into Darfur.