New York - Armed groups in the Central African Republic are using rape and sexual slavery to terrorise women and girls, led by commanders who appear to have ordered the assaults, Human Rights Watch said on Thursday.In a new report, the rights group documented 305 cases of rape and sexual slavery carried out against 296 women and girls, but these reflect only a fraction of the sexual violence, it said.The assaults were carried out from early 2013 to mid-2017, even as the large-scale violence that convulsed the country following the overthrow of Francois Bozize four years ago has subsided."Armed groups are using rape in a brutal, calculated way to punish and terrorise women and girls," said Hillary Margolis, women's rights researcher at Human Rights Watch. The report named six rebels in leadership positions who were identified by the survivors as having committed sexual violence or ordered their fighters to carry out the attacks.To date, the attackers have faced "no consequences whatsoever", said Margolis.Vigilante unitsOne of Africa's poorest countries, the Central African Republic descended into bloodletting in 2013 following the ouster of Bozize by a coalition of Muslim-majority rebel groups called the Seleka.In response, Christians, who account for about 80% of the population, organised vigilante units dubbed "anti-balaka" and violence between the two groups has led to thousands of deaths.More than a million people have fled their homes while 2.4 million people - more than half of the population - are in need of emergency food aid. "Commanders from the two main parties to the conflict have tolerated sexual violence by their forces: in some cases, they appear to have ordered and committed it," said the report on sexual violence in CAR.Weapon of war"At times, rape formed an integral part of armed assaults and was used as a weapon of war."Most of the documented abuses constitute war crimes, said the rights group. Some of the women were held as sexual slaves for up to 18 months, often subjected to repeated rape by multiple men, while others were forced to cook, clean and collect food as fighters' "wives".Thirteen women - three of whom were children when they were assaulted - said they became pregnant from the rapes.Human Rights Watch said a newly-established special criminal court set up in CAR should be up and running soon to hear cases of sexual assault. The UN peacekeeping mission Minusca should help authorities investigate cases of sexual violence and arrest those responsible for the crimes, the rights group said.