NEW YORK — A survey of dozens of women who fled violence in Darfur found that a third of them reported or showed signs of rape, and revealed a widespread fear of sexual violence in their refugee camp in Chad, a human rights group reported Sunday.

About half the rapes were carried out in Darfur by janjaweed militiamen allied to the Arab-dominated government in Khartoum, and half were assaults by Chadian villagers near the U.N. refugee camp, usually when the women left to search for firewood or herd livestock, according to the report by the U.S.-based group Physicians for Human Rights.

The group reached the 88 women included in the survey through camp leaders and by word-of-mouth — a sampling method the report said hinders drawing general conclusions about the prevalence of rape in Darfur or in the Farchana refugee camp in Chad.

Recording rape or interviewing victims of sexual violence is problematic in Darfur's Muslim culture, where women fear social stigma or further trauma and sometimes recant their allegations out of shame. Further complicating the effort, women displaced inside Darfur live mostly in government-controlled areas and fear reprisal.

The issue is highly contentious for the Sudanese government, which denies any systematic rape or violence against women.

The PHR survey supported widespread claims of rape often told by Darfuri refugees, and recounted by human rights and relief officials. U.N. officials said documenting the violence has become even more difficult following the Sudanese government's decision to expel 13 foreign aid groups, working mostly in Darfur.

The Darfur rapes fell into a common pattern, with a village overwhelmed by turbaned gunmen wearing green or khaki uniforms, often arriving on horse- or camel-back. Air strikes by the Sudanese military usually followed.

One woman from the Masalit tribe recounted how when she was 13, four Arab gunmen on horseback attacked her family's farm in a Darfur village, shot and killed her father, and raped her.

"When they shot my father, they saw I was a little girl. I did not have any energy or force against them," said the woman, now 19. "They used me. I started bleeding. It was so painful. ... I was sick for seven days. I could not stand up."

Physicians for Human Rights called for the prosecution of rape as a war crime and urged the International Criminal Court to issue warrants against Sudanese suspects. They also sought better protection for refugees in the Chad camps by Chadian police and international peacekeepers, including firewood-gathering patrols.

PHR said three doctors and a human rights researcher interviewed 88 women in November at the refugee camp in Farchana, Chad, where more than 20,000 Darfuris are watched over by some 2,000 Chadian soldiers, about 34 miles from Sudan's border.

Among the 88 women, 29 suffered "confirmed or highly probable rape," PHR found. Three women were assaulted twice, the group said.

The Darfur conflict began in 2003 when mostly ethnic African rebels in the western Sudanese province took up arms against the northern government in Khartoum, complaining of discrimination and neglect. The conflict has since claimed up to 300,000 lives and displaced 2.7 million people. About 250,000 have fled into Chad, where they live in refugee camps.