Gripping a pair of pliers, a doctor pried a bullet from Amina Kharim's swollen and bleeding left arm. Eight hours earlier, at dawn Tuesday, she had been asleep in a shelter of grass and sticks when government soldiers and police stormed into this camp of 5,000 in South Darfur.

Residents and relief workers said the troops burned shelters, smashed water pipes, fired tear gas and beat people as they fled half-asleep from their huts. Within five hours, they said, the camp was reduced to ashes and about 100 residents were crammed into the makeshift clinic, seeking first aid for gunshot wounds, burns and bruises.

"I saw the military coming and heard some shots. Then I felt pain and saw my arm bleeding. Now, my heart is burning with anger," said Kharim, 26, gripping her arm to steady it while the doctor worked in the shade of the mud-and-straw clinic. "There was a lot of blood, and then they started burning my hut. The world is not doing enough to protect us. We are so tired. Can someone please come help us?"

With violence still raging in Darfur's 20-month conflict between African rebels and pro-government forces, aid workers and camp residents said they feared Tuesday's pre-dawn assault was the beginning of a campaign to force displaced people back to villages where they could be vulnerable to further attack by Arab militias known as the Janjaweed.

Within a few hours of the attack, camp residents said, 250 families were placed in government trucks and moved under armed guard to an area 25 miles south. And at a nearby camp, Otash, officials removed an unknown number of residents and blocked access to aid workers.

"This was not supposed to have happened. This is forced relocation," complained Brig. Gen. Festus Okonkwo, a Nigerian officer from the African Union mission in Darfur. Okonkwo's team of 19 civilian monitors and 56 protective troops is based just eight miles from here, but he said news of the attack took him completely by surprise.

"They tried to remove them and they didn't want to go, so still they bulldoze the houses. No one was aware this was happening," he said.

At the United Nations, Jan Pronk, the U.N. envoy to Sudan, said there were "strong indications that war crimes and crimes against humanity have occurred in Darfur on a large and systematic scale," according to the Associated Press." In a report to the U.N. Security Council, he accused Sudan's government of failing to "end impunity" and bring to justice the perpetrators of widespread killings, rapes, looting and village burnings.

In Washington, the State Department spokesman Richard Boucher said the Bush administration "stands with the international community in holding the government of the Sudan responsible for the violations and requests immediate return" of the camp residents who were moved Tuesday.

Local officials defended the assault on al-Jeer Sureaf, saying they had been asked by the Sudanese government to remove people from the camps who had been stealing food from nearby communities. Some relief workers acknowledged that outsiders had been entering the camps to receive food and medical aid intended for residents displaced by war.

"The African leaders asked us to remove these people," said Mohammed Abdel Osman, an assistant to the governor of South Darfur in the nearby city of Nyala. "We did that service for them." But officials in Khartoum, the Sudanese capital, said they knew nothing about the incident and were investigating it.

Aid officials said they were puzzled by the officials' explanation, because the pre-dawn attack appeared aimed not at outside visitors but at the huts of camp residents who have fled war in other parts of Darfur. Some of those whose huts were torched Tuesday said they had escaped from villages that were attacked and burned by the Janjaweed.

As security conditions worsened, the United Nations halted food delivery operations in parts of South Darfur on Tuesday, cutting off aid to about 160,000 refugees in western Darfur. The United Nations also airlifted 88 aid workers out of South Darfur on Monday as a safety precaution.

"The space that we have for humanitarian activity is shrinking. It's a general trend downward, and it's very disturbing," said Barry Came, a spokesman for the World Food Program, a U.N. agency. "The security situation just continues to deteriorate."

The residents of al-Jeer Sureaf are among about 1.5 million Africans who live in squalid tent cities across Darfur after being driven from their farms by the fighting, which broke out in February 2003 when African tribes rebelled against the Arab-led government.

In retaliation, the United Nations says, the government has bombed villages and armed the Janjaweed militias. Tens of thousands of people have died from hunger, disease and violence; the Bush administration has described the crisis as genocide.

Worries over security have increased significantly since last month, when two aid workers from Save the Children were killed by a land mine. U.N. officials have blamed one of several African rebel groups for the attack. Tensions also increased when African Union monitors reported that 18 Sudanese of Arab origin were taken hostage while traveling on a bus last week.

Rebel groups deny setting the mines; they have also accused the Janjaweed of forcing 30 ethnic Africans from a bus on Sunday and shooting them. The African Union said it was investigating.

Pronk, of the United Nations, blamed rebels for stepping up attacks, harassing aid workers and stealing food from convoys. Some refugees said they believed the government assault here might be retaliation for stepped-up rebel actions.

"The incident of the mine is a very big concern. People who lay mines are cowards," Pronk said. "This kind of behavior has to stop because insecurity and violence [are] escalating. We are in a dilemma of increasing difficulties on the ground, increasing fighting, increasing number of people fleeing. But it's more difficult to help them because of the violence."

As camp residents here tended to their wounds and salvaged their belongings from smoldering huts, they described the ordeal that began at 3 a.m. when the troops entered their sleeping settlement. A midwife at the clinic said she had tied the beds of the maternity ward together and armed herself with knife.

Lying on a metal cot with several broken ribs, Taja Ibrahim, 28, writhed in pain and took gulps of air, her whole body heaving as she struggled to breathe. She said that the government troops had beaten her with sticks and guns but that she was too afraid of the Janjaweed to return home.

Nearby, Halima Hassan Adam, 21, cradled her newborn baby in her arms as she sat disconsolately outside their former home, now just a pile of singed straw. Her 3-year-old son's eyes still stung from the tear gas. The young mother bent down and searched the ground, hoping to save a few beans that had been crushed in the attack.

"I delivered my baby here 22 days ago," she said. "This was the only home we had. Now since yesterday, we have had no food or water. I am so scared. I am just holding my children tight and praying."

In the scorched camp, lizards scurried over charred blankets and donkeys nosed through the remains of shelters. But by dusk, women were starting to rebuild their homes, knotting vines of grass to long tree branches to make circular shelters. Meanwhile, aid workers filtered back into the community, surveying the ruins with horror.

"It makes you so angry you want to cry," said one worker, who spoke on condition of anonymity. "It's like the government wants to get rid of people in the town and send them to the desert where they are closer to death."

Staff writer Colum Lynch at the United Nations contributed to this report.

A doctor works to remove a bullet from the arm of Amina Kareem, who was sleeping in the camp when government troops began firing early Tuesday.A bicyclist rides through ruins of al-Jeer Sureaf. Residents said troops trucked out 250 families after the attack. Nawal Adam Ismael, 6, digs tent pole holes as mother Halima Hassan Adam searches rubble of their home. Watching is Nawal's brother Khalid Adam Ismael, 3. Halima Hassan Adam rests with her new baby in the devastated camp. "This was the only home we had," she said.Halima Osman rebuilds her home at the al-Jeer Sureaf refugee camp in Darfur. The women knot vines of grass to long tree branches to make circular shelters.