Halima Bashir, a young Sudanese woman who has been a victim of and witness to numerous barbaric acts in Darfur, has spoken out against the government in Khartoum with a hard-hitting account of the tragedy.

A member of the Zaghawa tribe, Bashir puts a human face on a situation where the number of casualties is so large as to be incomprehensible. The conflict between the Arab-dominated government in Khartoum and black Africans in Darfur, in western Sudan, has left about 300,000 dead and created as many as 2.5 million refugees, according to the UN.

Bashir, 29, said Tears of the Desert, written with the journalist Damien Lewis, who won an award for his reporting from Darfur last year, was her chance to speak out about the atrocities perpetrated by the Sudanese government against black Africans in Darfur.

"My story is not the only one," she said in London, where she lives with her husband and young son after a long battle to win asylum. "There are hundreds of thousands of other stories more painful than mine. With this book it is as if I'm telling this story for Darfuri women. I will keep on talking – it is the only thing I can give my people."

In Bashir, the victims of what the international criminal court has described as a policy of genocide by Sudan's leaders have found a soft-spoken but iron-willed representative.

Bashir arrived for our interview at a hotel in central London with her round, youthful face uncovered. But she was firm about not revealing her face to the world, particularly to the Sudanese authorities. While she remains safe in Britain, she fears for the safety of her mother, sister and two brothers, who joined the rebels in Darfur.

She still does not know what happened to her family after they fled their village when government troops and the notorious Janjaweed militia attacked. The men of the village stood and fought to buy time for the women and children to flee to the forest. Her father died in the attack. Bashir does not want the Khartoum government to use the knowledge of what she looks like to track down her family – if they are still alive.

Because of fears for her family, Bashir talked to us with her face covered by headgear, hastily purchased around the corner from John Lewis. Only her eyes were visible during the interview.

Tears of the Desert is not just an account of the atrocities committed by the government-backed Janjaweed – or devils on horseback – against black Africans. The first half of the book describes a happy childhood in a close-knit Darfur village, although it does not gloss over Bashir's hideous circumcision at the age of eight.

For the most part, however, growing up was a happy time for Bashir. Family scenes that feature her much-loved grandmother and her best friend, Kadiga, are vividly brought to life. Like little girls anywhere, Bashir played with dolls, although these were rag dolls made from old clothes stuffed with straw.

Her father had big plans for Bashir and she was the first girl from her village to go away to school. Eventually she became a doctor, but she ran into trouble with the authorities for telling a reporter that the government should help all Darfuri people regardless of their tribe.

As punishment she was transferred to Mazkhabad, a village in the remote north of Darfur, and put in charge of a clinic. This is where she saw and experienced at first hand the atrocities of the Darfur conflict. Not even in her darkest nightmare had she imagined she would witness such horror, she wrote, as she treated girls as young as eight who had been repeatedly raped.

Bashir had to care for more than 40 girls who were sexually assaulted at their school while government soldiers cordoned off the premises. Parents were kept standing outside the school as their daughters' screaming pierced the air.

A rape victim who was a teacher told Bashir: "They were shouting and screaming at us. You know what they were saying? 'We have come here to kill you! To finish you all! You are black slaves! You are worse than dogs. The worst was that they were laughing and yelping with joy as they did those terrible things."

The Janjaweed eventually came for Bashir herself. Three men in khaki uniforms took her from the clinic to a military camp, where she was beaten and repeatedly raped. The ordeal went on into a second day with Bashir retreating in her head "to a faraway place where my God had taken me, a place where they couldn't reach me".

One of her captors told her: "We're going to let you live because we know you'd prefer to die. Isn't that clever of us? Aren't we clever, doctor? We may not have your education, but we're damn smart, wouldn't you agree?"

Hard as it was for her to go over such painful memories, Bashir said the process of writing her memoir help her come to terms with her terrible ordeal. More importantly, she wanted to tell the whole world about what was going on, especially the atrocities committed against young girls.

"These men were not normal," she said. "No normal people would do such a thing to children. I wanted to tell the whole world what was happening."

She could only explain the actions of the aggressors as an extremely virulent form of racism.

"It is because of the colour of our skin, it is because we are black," she said. "Even at school they give us nicknames and make jokes about us. It is something that has gone on a long time."

Bashir cited her experience at medical school where she had a reputation as a swot. The corpses students worked on were exclusively black. One of her friends said: "Arabs do not give a damn about us when we're alive, and even less when we're dead".

Some foreign policy commentators have criticised the international criminal court's decision to charge Omar al-Bashir, the Sudanese president, with genocide and crimes against humanity. They say it will make a peace deal between the Sudanese government and the rebels harder to achieve and warn it could jeopardise the already troubled deployment of a joint UN-African Union peacekeeping force in Darfur.

Bashir, however, has no reservations about the court's decision. She told an audience at the Royal Festival Hall: "I can't explain how happy I am for the ICC case," she said. "It is now more than five years this has been going on and very little has been done. It's as if we've been talking to deaf people. For me this is a step for justice."

· Tears of the Desert, by Halima Bashir, written with Damien Lewis, is published by Hodder & Stoughton.