Armed fighters in the Central African Republic (CAR) have used sexual violence to "terrorise women and children" as a tactic of war during the nearly five-year conflict, Human Rights Watch (HRW) has claimed.

Fighters beat women, burned them and left them with broken bones, smashed teeth and head wounds, the New York-based rights group said in a report on Thursday, citing testimony.

Survivors said they were raped by up to 10 or more men during a single incident.

According to the report, there have been 305 cases of rape and sexual slavery against 296 women and girls by members of armed groups between early 2013 and mid-2017.

Members of the mainly Muslim Seleka and Christian Anti-balaka forces - the two main parties involved in the conflict - have used sexual violence as revenge for perceived support of rivals, HRW said.

READ MORE: UN 'botched' sexual abuse cases in CAR

"Armed groups are using rape in a brutal, calculated way to punish and terrorise women and girls," said Hillary Margolis, HRW's women's rights researcher, in a statement.

She added: "Every day, survivors live with the devastating aftermath of rape, and the knowledge that their attackers are walking free, perhaps holding positions of power, and to date facing no consequences whatsoever."

According to HRW, most of the abuses not only violate CAR's laws but also constitute war crimes, with some possible crimes against humanity.

The group reported that only 11 of the 296 survivors interviewed had tried to initiate a criminal investigation.

So far, no member of any armed group has been arrested or tried for committing sexual violence.

'Inaccessible justice'

Lewis Mudge, a researcher in the Africa Division at HRW, told Al Jazeera on Thursday that "almost nothing is happening to survivors of these attacks and little is being done to prevent them".

"Survivors of sexual violence need to be given support - medical, psychological and social," he said.

A new government organisation, the Mixed Unit for Rapid Intervention and Suppression of Sexual Violence against Women and Children, is trying to address the plight of survivors.

"If those that we know are responsible for these grave crimes - of rape and violation of human rights - if they are not arrested right now and taken into custody, no victims will have the will to seek justice and that makes justice inaccessible," said Paul Amedee Moye, head of the group.

He added: "You have to talk about zero impunity."

CAR, a former French colony, fell into a protracted political crisis in 2013 after President Francois Bozize was overthrown by the Seleka group, who in turn were driven from power.

READ MORE: Is the UN sending the wrong people to keep the peace?

Seleka's abuses against the Christian population led to the emergence of self-defence groups - the Anti-balaka - which embarked on their own campaign of violence.

The fighting has killed thousands of people and forced nearly half a million from their homes.

The CAR government struck a peace deal with 13 of the 14 armed groups active in the country on June 19.

The truce was shortly followed by violent clashes between rival factions which killed more than 100 people in the town of Bria, northeast of the capital, Bangui.

UN peacekeeping mission

MINUSCA, the United Nations peacekeeping mission, has operated in the country since April 2014.

UN peacekeepers in CAR - a total of 13,000 - have also been embroiled in a series of sexual allegations.

According to a recent investigation by the Associated Press news agency, between 2004 and 2016, the UN received almost 2,000 allegations of sexual exploitation and abuse against its peacekeepers.

READ MORE: Why do some UN peacekeepers rape?

Vladimir Monteiro, MINUSCA spokesman, refused to comment on the findings of the HRW report because he had not seen it by the time of publication.

But he told Al Jazeera on Thursday that his team reports on human rights violations on a weekly basis and that special units monitor violence against women.

"Women and vulnerable people are our main focus with respect to peace and the protection of civilians, Monteiro said. "We really care about women and vulnerable people in CAR."

HRW's Mudge urged MINUSCA to be "proactive" and think to protect women and girls before they are attacked.

"Protection should not only be reactive," he said.

Additional reporting by Saba Aziz: @saba_aziz