By Will Ross
BBC News, Nairobi
Rape has been used as a weapon of war in Dr Congo
More than half of the victims of rape in the east of the Democratic Republic of Congo were gang raped by armed men, a report says.
For years rape has been used against women in the region but the report reveals the scale of the problem.
More than 4,000 rape victims were interviewed over a four-year period.
The authors of the report, commissioned by Oxfam, say there is also evidence suggesting a dramatic rise in the number of rapes by civilians.
It comes at a time when there is debate over how long the United Nations peacekeeping force should remain in DR Congo.
The extensive research, carried out by the Harvard Humanitarian Initiative, in the eastern South Kivu province produced shocking findings.
It shows that 60% of the rape victims were gang raped by armed men and more than half of the assaults took place in the victims' homes.
There was also evidence of a large increase in the number of rapes carried out by civilians.
Back in 2004, 1% of rapes were committed by civilians, the report says.
Four years later they were responsible for more than a third of these attacks.
The researchers say this proves that the scale of rape during years of war in DR Congo has made this crime seem more acceptable.
Oxfam says given the insecurity in DR Congo, it is imperative the UN peacekeepers stay.
The UN troops have been backing efforts to defeat rebels linked to the 1994 genocide in Rwanda.
However research shows that when these UN-backed offensives are carried out, women become even more vulnerable.
The rebels and the government troops use rape as a weapon of war to punish civilians.
The victims face terrible stigma and this new study reveals that more than half of the women waited at least a year before seeking treatment.
War-torn South Kivu is home to five million people but there is just one hospital which can offer suitable help to victims of rape.
Oxfam wants the world's richer countries to help increase the medical services available for survivors of sexual violence in Congo.
Last year alone the UN says more than 5,000 people were raped in South Kivu.