ON THE SUDAN BORDER -- They strike without warning, thundering into villages on horses and camels, cutting down with swords and bullets those who try to flee. In their wake they leave bombed and burned-out homes.
After more than 16 months of terror, a promise by the Sudanese president to disarm the mostly Arab Janjaweed militias does not reassure the more than 1 million black Africans chased from their homes in attacks that human rights groups say amount to ethnic cleansing. Some aid workers question whether the government is able to fulfill its pledge.
Nomadic Arab tribes have long been in conflict with their African farming neighbors over Darfur's water and usable land. The tensions exploded into violence when two African rebel groups took up arms against the government in February 2003 over what they regard as unjust treatment by the government in their struggle with Arab countrymen.
The rebel Justice and Equality Movement and the Sudan Liberation Army accuse the government of arming the Janjaweed, a name translated as "horsemen" in the local dialect. The government denies any involvement, but across the region, refugees describe how Sudanese airplanes and helicopter gunships back the militia attacks.
Residents of the North Darfur provincial town of al-Fater claim a nearby military garrison was handing out cash and identity cards to Arab herders a year ago, when rebels were advancing in the area.
"Soon after, we heard on the radio that the Janjaweed were causing havoc," one resident said. He asked not to be named for fear of retribution.
U.N. Secretary-General Kofi Annan, in a diplomatic push with Secretary of State Colin Powell last week, won a commitment from President Omar el-Bashir to contain the militias and allow human rights monitors into Darfur.
The United States has raised the possibility of sanctions if the government fails to stop the attacks and allow international aid to reach the displaced.
Up to 30,000 people have been killed in the uprising, and the U.S. Agency for International Development predicts the number could surge to 300,000 if aid doesn't reach the estimated 2 million in desperate need. Aid workers say Darfur has become the world's worst humanitarian crisis.
"What matters now is the implementation" of the agreement, said Jasmine Whitbread, international director of British aid group Oxfam. "Time is running out."
The Sudanese refugees have heard promises before. When the government and rebel groups signed an April 8 cease-fire, some returned to the ruins of their villages to rebuild -- only to be attacked all over again.
There wasn't even time to bury the bodies, which were left where they fell, said Abel Chatter, who returned to the Chad border town of Birak less than two weeks ago.
"If we go back now, it will be the same thing all over again," said Khatir, a tall man in a white turban and dark sunglasses. He is trying to make enough to feed his wife and three children by selling straw at the market.
Even if el-Bashir's government is serious about disarming the militias, some humanitarian workers in Darfur privately questioned their ability to contain the armed bands, which roam a vast and desolate region the size of France.
In previous disarmament efforts in Liberia and Sierra Leone, fighters lay down their weapons only to pick them up again soon after because they could find no better work.
Jan Egeland, U.N. under-secretary-general for humanitarian affairs, concedes the situation is "a nightmare."
"The only thing there is an abundance of now in Darfur is arms. It is easier to get a Kalashnikov than bread," he told reporters on a tour of Sudan and Chad with Annan last week.
Sudanese Foreign Minister Mustafa Osman Ismail told reporters last week that 6,000 soldiers and policemen would be deployed in Darfur to improve security, but he did not say when or where they would come from.
"What we don't want is to see these same people in police and security force uniforms now," Egeland said of the Janjaweed.
Annan says robust monitoring by international observers will be key to resolving the devastating conflict.
But Mohammed isn't taking any chances. Sitting on a bag of millet amid a throng of refugees, he waited with his head in his hands to board a U.N. truck to a refugee camp deeper in Chad.