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.

“He will never get rid of the Janjaweed,” said Mohammed Ahmat Mohammed, one of the more than 200,000 Sudanese sheltering in neighboring Chad. “He just wants us to go back so he can kill us all.”

Mohammed watched helplessly as the armed horsemen who overran his village late last year stole his cattle, set fire to his home and shot his 28-year-old son dead.

He, his two wives and 15 surviving children fled over the border with only the clothes on their backs. They have huddled for the past nine months under the thorn trees, which offer little protection against the beating sun, swirling sand storms and sudden downpours of one of the world’s most inhospitable regions.

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 African Union on Monday said it would send 300 peacekeepers to Darfur to protect the growing number of refugees.

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.”