Sudan's pro-government militias are using mass rape as a weapon in their conflict against non-Arab groups in Darfur, says Amnesty International.
More than a million people in Sudan have fled their homes
Girls as young as eight and women of 80 have been raped, says the human rights group, which wants an enquiry into war crimes and crimes against humanity.
Peace talks between the government and Darfur rebels broke down on Saturday.
Aid agencies have warned that thousands could die from hunger and disease in the camps, where civilians have fled.
Amnesty accuses the international community of not doing enough to protect women in Darfur and also in refugee camps in neighbouring Chad, where many have fled.
The human rights group also directly accuses the Sudanese government of supporting the attacks by the Janjaweed militia.
But in a BBC interview, the Sudanese ambassador to London, Dr Hasan Abdin, denied his government was complicit in the attacks and described Amnesty's evidence as "flimsy and exaggerated".
He called for a thorough investigation into any sexual abuse in Darfur.
"Rape crimes need to be investigated in a very thorough manner in a court of justice and not in reports by reporters," he said.
In its report Rape as a Weapon of War, Amnesty publishes the testimonies of some of the hundreds of women its researchers have spoken to.
"I was sleeping when the attack on Disa [village] started. I was taken away by the attackers, they were all in uniforms," said a female refugee from Disa.
"They took dozens of other girls and made us walk for three hours. During the day we were beaten and they were telling us: 'You, the black women, we will exterminate you, you have no god.' At night we were raped several times. The Arabs guarded us with arms and we were not given food for three days."
In many cases, women have been raped in public, in front of their husbands, relatives, or the wider community, Amnesty says. This is in order to humiliate them, their family and the entire group.
Amnesty adds that even in refugee camps, women are not safe from sexual violence.
It says that almost all of the rapes were carried out with either the direct involvement or in view of government forces and yet no-one has been charged with rape or abduction.
One woman said she was raped outside a refugee camp in western Darfur in June 2004. She reported it to the police and the men were arrested and disarmed.
But she says their weapons were returned the next day following the intervention of Janjaweed leaders and she was told not to make any further reports.
She regularly sees the men who raped her in the market.
Amnesty calls for an international commission of inquiry into the conflict in Darfur, including claims that the widespread rapes are part of a campaign of genocide against the region's non-Arab population.
Tens of thousands of people have been killed in Darfur, and more than one million have fled their homes in the face of militia attacks.