Pascaline, 16, with her baby at MSF's Seruka clinic in Bujumbura. She was raped as she worked in the fields and has chosen to talk about her ordeal despite taboos surrounding the issue. Photograph: Linda Nylind  

The football fans were making a noisy exit from the city stadium as Esperence picked up a bundle of food and began walking along the river to visit her brother in hospital. It was 5pm on Saturday and Interstar had just played Muzinda FC in a friendly in Bujumbura.

In the rolling green hills above Burundi's capital rainclouds gathered as a teenage girl, Hilaire, picked up a bucket to fetch water for her family.

After 12 years of civil war peace might appear to have settled upon this tiny central African country. But for the women the violence is not over. Within minutes of each other on that recent Saturday, Esperence and Hilaire became the latest victims of the sexual aggression that pervades an impoverished, war-ravaged society.

Esperence saw the first man appear in front of her as she walked along the banks of the Ntahangwa river, in the north of Bujumbura. "He put out his hand and said, 'How are you?' Then I was grabbed from behind by another man, he put his hand over my eyes and pulled me to the ground. I tried to scream but he put his hand over my mouth. He held me down and tore my clothes off. He had sex with me, he ejaculated inside me. The other man, his friend, was shouting, 'How does she feel?' Then he raped me, too."

Hilaire's attack was just as brutal. Stopped by a soldier as she walked with her six-year-old brother to the well in her village of Mubone, she was ordered to halt and was raped. She is only 13.

Two days later, Hilaire and Esperence sat silently in the waiting room of a women's health clinic, run by Médecins sans Frontières, in Bujumbura. Around them sat 20 other women and girls - the collateral damage from the weekend in a society that has no word for rape in the local language, Kirundi. In a country where up to 400,000 people have HIV, the widespread sexual violence is not only brutalising - it can be deadly.

"Rape contributes hugely to the spread of HIV," said Fabio Pompetti, head of the local MSF mission. "The men never use condoms and the fact it is brutal by necessity, a forced act, makes it much more likely that you get infected."

Every month more than 100 women overcome the taboos surrounding sexual violence to make their way to the clinic, where the sign outside reads Seruka, or "rise from darkness".

Esperence described to a doctor how she was told about Seruka shortly after her attack. "I was lying on the ground and another woman saw me and came to help me," she said. "When she heard what happened she told me about this place and told me to come quickly."

Timing is important. The clinic hands out anti-retroviral drugs which, if taken within 72 hours of the rape, have an 80% chance of preventing HIV. Slowly, the message is reaching local women. But the fear of rejection by their husbands and families if they are open about being raped still keeps many away.

Hilaire's mother, Veronique, told an MSF psychologist how her gregarious daughter had hardly spoken since the attack. "We knew the man - he is a soldier," she said. "We went to the military and, because we knew him, they found him and put him in prison."

Few see their attackers behind bars, however. The police investigate a rape only if the attacker is known to the victim. The lengthy legal process and the publicity it attracts deters most women from going to the police.

Esperence, a single mother, shook her head and wept when a counsellor had asked whether she knew her attackers. She listened intently as a nurse later described how to take her ARV treatment. She smiled for the first time.

"She is one of the courageous ones. She has come here to talk about what happened. Many are too scared to do that," said a doctor. Esperence and Hilaire were given an appointment for an HIV test in three months' time. The results will be followed up by clinic staff.

As they left they passed Pascaline, 16, sitting under a poster saying: "Your only weapon against the violence is to speak out." Like the other two, she had heard about the clinic and chosen to do so.

Holding her two-month-old baby, she said she had been attacked that day. "I was working in the fields. A man came up and demanded money. He was holding a knife, When I said I had none, he pushed me to the ground, put the knife against my throat and he raped me."