They came out of the forest. Men with guns appearing barely human to the frail, ageing woman who months later recounted her ordeal, bent double after surgery to save her womb.

"They didn't look like men. Their skin was covered in cuts. Their clothes were completely torn. They became someone else, not humans," she said at a hospital in the often fought-over town of Rutshuru in eastern Congo.

But the woman still recognised the men who descended on her village as members of the Mai Mai ethnic militia. Their preference for wearing animal skins and amulets, popular for their supposed magical powers of protection, distinguished them from the government soldiers, foreign rebels and other armed gangs who have also contributed to the wholesale rape of hundreds of thousands of women and girls over more than a decade of conflict.

It took months for the 58-year-old woman from Kindu to reach Rutshuru hospital for treatment and to tell her story. The Mai Mai shot her husband when he didn't have any money to hand over. When her children screamed they shot them too. Then the woman was raped by five men. One of her attackers nearly destroyed her womb by thrusting his gun into it. She fled her village. As she travelled to Rutshuru she was raped again, this time by Rwandan Hutu extremists who fled to Congo after leading the genocide in their own country.

"It is impossible to live in safety. They have murdered my children, they have murdered my husband. They have raped me so many times. I do not know who is alive and who is dead in my village," she said.

Hers is not an unusual account from survivors of villages in eastern Congo subjected to repeated attacks in which women and girls were serially raped and the men killed. Health clinics in the region treat tens of thousands of women for sexual assault every year, and doctors say that is a fraction of those who were attacked. Last year, Médecins Sans Frontières estimated that 75% of all the rape cases it dealt with worldwide were in eastern Congo. Many young women have been abducted into sexual slavery. In some villages, armed groups kill the men and rape all the women. Many are left HIV positive and pregnant. In some larger towns, such as Shabunda, Congolese human rights groups estimate seven out of 10 women have been raped.

Mutilation

Doctors say the onslaught against women is notable not only for its scale but for its brutality. Gang rapes are commonplace and frequently accompanied by torture in which women are mutilated by having guns or stakes thrust into their vaginas, or their genitals slashed with knives. One in four who make it to hospitals in Goma and Rutshuru require major surgery. More than a third are teenagers.

Human rights groups say that while rape is a product of many conflicts, its systematic nature in Congo makes it a "weapon of war" used to terrorise and punish communities or as a tool of ethnic cleansing.

Immaculee Birhaheka, the head of Paif, a women's rights group in Goma, said almost no woman outside of a few major towns is safe. She describes what happened in a string of villages along the rudimentary road south from Goma toward Bukavu, 75 miles away. "The women who come from there tell us that every woman in every village has been raped over the years. There is not one who was not attacked, they told us. Some of them were captured and taken into the forest for months, even two years. When they are released some are in such bad condition that they die.

"The women don't talk about it as a weapon of war but they say they are seriously targeted, that it is very organised. It's clear from the behaviour of the soldiers that they have permission to attack women. Their commanders do not stop it and may even order it."

One of those commanders is Colonel Edmond Ngarambe who serves in the Democratic Front for the Liberation of Rwanda (FDLR), an armed group of Hutu exiles born out of the Interahamwe militia that led the genocide in Rwanda. The FDLR controls about 40% of the territory in the two Congolese provinces worst hit by conflict, North and South Kivu.

Last year, in a village south of Bukavu, he admitted his men were responsible for systematic sexual assaults on women. "This thing of rape, I can't deny that happens. We are human beings. But it's not just us. The Mai Mai, the government soldiers who are not paid, the Rastas do the same thing. And some people sent by our enemies do it to cause anger against us," he said.

That many other groups - from the Mai Mai to Tutsi rebels and the Rastas, a group of defectors from the likes of the FDLR - are also responsible for mass rape is not in doubt. But around Bukavu the victims tend to point the fingers at Ngarambe's men.

It may be no coincidence that rape was an integral part of the mass killings in Rwanda 14 years ago. The international tribunal trying those responsible for organising the genocide made a landmark ruling that for the first time defined rape as an act of genocide under international law if it is part of a systematic move to wipe out an ethnic group.

But others too are responsible. Forces under the command of the rebel Congolese Tutsi general, Laurent Nkunda, who recently seized swaths of territory in North Kivu, have a long history of assaults on women. Three years ago they attacked Bukavu. A Human Rights Watch report said Nkunda's forces "went house to house raping and looting". Among the victims were teenagers and three girls of three years old.

Retribution

MSF says that "while rape is etched into the general framework of violence", it's also seen as legitimate "additional retribution" by the armed groups against civilians who fail to hand over food or are perceived as supporting their enemies.

Many women have to make the appalling choice between risking rape by venturing out of their villages to tend their crops in order to feed their children, and seeking a modicum of protection in numbers but risking starvation. Among them is a 23-year-old woman from Walikali. She is small, thin-faced and her eyes dart about constantly.

"There were four of us. I was looking for food. There were seven Interahamwe and they took us. Two of us tried to run away. They shot at them. One was shot through the chest and died. The other got a bullet in the leg. They raped her," she said. "I fainted because there were seven of them and it was too hard for me. When they left it was raining. Our families came looking. We were all bleeding. We were almost dead."