Gelu, Sudan -- At the edge of a windswept landscape in Darfur, near Sudan's porous, 800-mile border with Chad, Khalia Daoud squats in the shade of her small straw hut along with hundreds of other Chadian refugees, mostly women, children and the elderly.

Her tiny makeshift shelter, like those of her neighbors, provides little protection from the desert's chilly nighttime winds. Donkeys mill about, and under the shade of a nearby thorn tree a few women display a meager assortment of root vegetables, millet, peanuts and spices in the encampment's only market.

A mother of six, Daoud fled from Chad to Darfur more than a month ago. She has received little help from aid agencies, which are reluctant to travel amid the increasingly dangerous security situation. Still, she is glad to be free from the violent turmoil in her village. "It seems as if we are welcome here. No one has harassed us yet," she said.

But the trouble from which she fled may have followed her. Operating from bases inside Sudan, Chadian rebels have begun launching cross-border attacks on their home country. Since their first major attack, on the eastern city of Adre in December, their numbers have grown to between 8,000 and 9,000 well-armed men.

A similar number of Chadians have sought refuge in western Sudan's dangerous Darfur region, fleeing attacks from rival tribesmen backed by the ailing, beleaguered president of Chad, Idriss Deby, and his non-Arab tribe, the Zaghawa.

The emergence of cross-border rebels is a new and alarming development in Darfur, where more than 200,000 Sudanese have died, largely at the hands of government-backed Arab militias, and another 2 million have endured famine and displacement.

The proliferation of rebel groups, the rising tensions between Chad and Sudan, and the enmity between the tribes that live on both sides of the border are making things even worse for those caught in the middle.

"In Chad, the Zaghawa and Massalit tribes take anything from us they want, and you can do nothing," Sheikh Ibrahim Osman, 30, said at one of the encampments along the border inside Darfur. "I hear that the problem here in Darfur is the same, only in reverse."

International aid agencies, which must negotiate safe travel with each rebel group, put much of the blame on the government in Khartoum.

"We are working with a sovereign country that are owners of this land. They should ensure our safety," says Andy Pendleton of the U.N. Office for the Coordination of Humanitarian Affairs in West Darfur, referring to the Sudanese government. "We shouldn't have to deal with fighting forces that have commandeered a piece of the pie."

Two weeks ago in western Darfur, a Chronicle correspondent visited a Chadian rebel base situated past two burned-out villages near the border.

Forty new Toyota Land Cruisers lined the edge of a dust-choked field. Tethered to the sides of the Land Cruisers were sacks filled with rocket-propelled grenades. Hundreds of young rebels in new, if mismatched, uniforms carried Kalashnikovs over their shoulders and belts of bullets around their torsos.

"I am not a politician and have no intention for being a politician," 35-year-old rebel leader Muhammad Nour said. "What we want to do for Chad is kick out President Deby, if he refuses to sit down with us and others."

Nour decried the corruption he said was rampant within Chad and laid out a vision for a transition to democracy. But among the rebels at the camp were members of various Arab militias as well as black African tribesmen.

Nour's assessment of the Darfur crisis -- which Western governments have labeled genocide and laid squarely at the door of Sudan President Omar el-Bashir's government -- was similar to explanations routinely offered by officials in Khartoum.

"There is no Sudanese rebellion. It is all a tribal problem," Nour said dismissively. He insisted that the only support he was getting from Sudan was free access.

"Our weapons come from other governments in Africa, and Sudan allows them to be transported here," he said without elaborating.

Deby, Chad's president, has long supplied the Darfur rebels, in particular the Sudan Liberation Army, with arms, ammunition and safe passage through Chad.

A U.N. report released in late January said Libya and Eritrea also are providing arms, ammunition and financial and political support to the Darfur rebels, in defiance of a U.N. Security Council embargo on arming groups in the Darfur region.

"It is very naive for some people to speak about intervention in (Sudan's) affairs," said Eltayeb Hag Ateya, head of the Peace Studies Institute at the University of Khartoum. "It is not your affairs -- it is the affairs concerning the Zaghawa or the Tama or the Massalit tribes."

Back at the refugee camp along the border, Khalia Daoud knows this all too well. "It's hard to tell the sides apart. All of the villages are mixed," she said. But her tribe is on the side of the rebels, so she and her children prepared to spend another night in a foreign country.