Amnesty International says women and girls are being targeted in conflicts around the world while the authorities do little or nothing to prevent it.
Violence against women can be part of a deliberate plan, the report says
In a report called Lives Blown Apart, the organisation says these crimes persist because those who commit them know prosecutions are rare.
Despite promises, treaties and legal mechanisms, governments have failed to protect women and girls, Amnesty says.
It cites conflicts in Colombia, Iraq, Sudan, Chechnya, Nepal and Afghanistan.
The human rights group says its investigations have found that violence against women is not just a by-product of war, but often a deliberate military strategy, with women particularly targeted in ethnic cleansing campaigns.
"Women and girls are not just killed, they are raped, sexually attacked, mutilated and humiliated," said Irene Khan, secretary general of Amnesty International.
"By attacking the women you are attacking the honour of your enemy, you demoralise the men, you scare people into running away," she said.
In addition to women being deliberately targeted, they are also the main victims of so-called "collateral damage", by "precision" bombing or landmines, says the report.
It says social restrictions on their mobility or domestic responsibilities may mean women are less able to flee when the civilian population comes under fire.
The study lists 36 current conflicts in which women are being targeted by male combatants.
"In the community, they made such fun of me that I had to leave the village and live in the forest.. I am hungry, I have no clothes and no soap," Sanguina, a woman raped twice during the conflict in DR Congo, told Amnesty.
"I don't have any money to pay for medical care. It would be better if I died with the baby in my womb."
In Colombia, the report says women have been horrifically attacked by both sides in the civil conflict.
In the Indian state of Gujarat, in clashes between Hindus and Muslims, pregnant women had the babies cut out of their wombs.
And in the conflict in Liberia, between 60% and 70% of women suffered some sort of sexual assault.
The report demands that governments - who sometimes cite women's plight as justification for military intervention - must realise their responsibilities to protect women's rights and provide services for women if they do intervene.
Ms Khan says it is essential that one of the first prosecutions by the International Criminal Court when it begins functioning next year includes crimes of violence against women.
However, she says the court cannot deliver justice without political support. Ms Khan is calling on world leaders to "do more than just make pious statements condemning rape and sexual violence".
Amnesty is presenting an agenda for action at international, regional, national and local levels, said Ms Khan.
"We have to mobilise global outrage - to challenge the violence, support those women who suffer and put pressure on those who can bring about change."