Cox's Bazar, Bangladesh - Twenty-year-old Ayesha Begum sat on a plastic mat inside her family's bamboo and tarpaulin shelter in the sprawling makeshift refugee settlement of Balukhali.

She cradled her one-year-old son in her arms, blowing on his face every so often to give him some relief from the sweltering heat.

"I was raped just 13 days ago," said the Rohingya refugee.

Ayesha, who arrived in Bangladesh less than a week ago, said she was eating dinner with her four sisters-in-law in their village of Tami in Myanmar's Buthidaung Township when army troops attacked the hamlet. Soldiers entered their home and forced the women into a room.

READ MORE: Scores of Rohingya feared drowned after boat capsizes

They ripped Ayesha's baby from her arms and kicked him "like a football".

Ayesha said the soldiers stripped the women naked. A soldier held a knife to her throat and began to rape her. Twelve soldiers took turns to rape the women over the course of what she believes was several hours.

"I felt like they would kill me," said Ayesha, her dark eyes alert. "I was afraid my child was dead," she added, running a hand over his head.

Speaking in the presence of her mother, brother, sister and husband, with nothing but bamboo slats and plastic-sheet walls dividing them from their neighbours on either side, Ayesha said it took eight days to walk to Bangladesh.

While fleeing Myanmar, two of her sisters-in-law who had been raped with her died. "They were so weak they died," she said.

For more than a month, the Myanmar army has waged a brutal military campaign in northern Rakhine state against the Rohingya - a Muslim-majority ethnic group to whom the Myanmar government denies citizenship and basic rights - after fighters with a Rohingya armed group carried out attacks on security forces on August 25.

The Myanmar army has carried out a number of such offensives since the 1970s, during which Rohingya have reported rapes, torture, arson and murder. The United Nations has called the latest military offensive ethnic cleansing.

More than 501,800 Rohingya have fled the Buddhist-majority country and crossed into Bangladesh since August 25. Densely populated refugee settlements have mushroomed around the arterial road in Bangladesh's Cox's Bazar district that borders Myanmar.

The refugees, the majority of whom are women and children, are in desperate need of humanitarian aid, including shelter, food, sanitation and medical care. Many women and girls were raped and sexually assaulted by Myanmar army soldiers.

Survivors and witnesses have shared accounts of women and girls being raped then locked inside houses that were torched. They have recounted stories of torture, mutilations, being stripped naked and other atrocities and acts of humiliation.

"[Soldiers] entered our house and they took away our sister. She was very beautiful," said Mohsina Begum, 20, also from Tami village. She said soldiers sexually assaulted and attempted to rape her until the village chairman intervened.

While Mohsina and her family were fleeing, they found the body of her 19-year-old sister, but couldn't stop to bury her.

Rajuma's story: 'They ripped my son from me and cut his throat'

Rajuma Begum, 20, survived the August 30 massacre in Tula Toli, believed to have been one of the most brutal incidents of Myanmar army violence. Villagers were taken to a beach by the river where the men were separated from the women and children and then gunned down, hacked to death and bayoneted.

Rajuma was holding her son, Mohammed Saddique, in her arms, when four or five soldiers began taking women away in groups of five to seven.

"They took me along with another four women inside a house," Rajuma recounted, speaking at a school in Kutupalong refugee camp.

"They ripped my son from my arms and threw him [on the ground] and cut his throat," she said, before burying her head in her hands and starting to wail.

"I am thirsty to hear someone calling me 'ma'," Rajuma said between sobs. "I had a younger brother who is 10 years old. I'm sorry to him because they took him and I couldn't save him."

READ MORE: How Myanmar expelled the majority of its Rohingya

Rajuma was held in a room with three other mothers, one teenage girl and one woman who was about 50 years old. The soldiers raped them all except the older woman. Rajuma was raped by two men for what she said felt like two or three hours.

Afterwards, they beat the women with wooden sticks, then flashed torches on them three times to make sure they were dead. The soldiers locked them inside the house and set fire to it.

It was the heat from the blaze that made Rajuma regain consciousness. She was able to break through the bamboo walls and escape. She hid on a hill for a day and when she came out on the other side encountered three other women from her village and an orphan.

Naked, she dressed herself in clothes abandoned by fleeing Rohingya. When she crossed the border, a Bangladeshi helped her get to Kutapalong where she was treated at a clinic. In Bangladesh, she was reunited with her husband Mohammed Rafiq, 20, who had survived by swimming across the river before the massacre in Tula Toli began.

"My family members were killed, and now there is only me, my brother and my husband here. I want to share this with all the world so they can bring some peace," said Rajuma, who has scars from being beaten on her chin and on the right side of her head where her hair has been shaved and is hidden by a red headscarf.

"The military killed seven of my family members. My mother, Sufia Khatun, 50 years old, Rokeya Begum and Rubina Begum, one of them was 18, and the other was 15, both of my sisters were taken by the army and raped and killed. Musa Ali, my brother, 10 years old, I am guessing he died, and my sister-in-law Khalida who was 25 years old, and her son Rojook Ali, who is two a half years old, and my son Mohammed Saddique, who was one year and four months."

Rajuma said: "It's important to know our story, what happened to us as the Rohingya."

Echoes of Rwanda genocide

Peter Bouckaert, emergencies director at Human Rights Watch who investigates war crimes and crimes against humanity, said in an interview the group is collecting data on "what is happening across the border as this ethnic cleansing campaign continues against the Rohingya people" with the intention of prosecuting those responsible for the crimes.

"In my 20 years working at Human Rights Watch, these are some of the most shocking and horrific abuses that I have documented. They really bring back memories of the genocide in Rwanda in terms of the level of hatred and extreme violence shown - especially towards women and children," he said.

"We're seeing pretty widespread rape and sexual assault on women," Bouckaert explained.

READ MORE: 'Lost and found booth' reunites Rohingya families

"The majority of the women who were raped were killed. There is no doubt about that," he said, adding that "racist hatred" is the motivation behind much of the violence.

"[The] campaign of dehumanisation and racism against the Rohingya is really what is driving this extreme violence, including sexual violence, against the community," he said, referring to how officials have long stigmatised the Rohingya as "terrorists", or too "dirty" for soldiers to rape.

"This campaign of hatred ... really does remind us of what happened with Tutsis in the Rwandan genocide, who were called 'cockroaches' by their government. You know these kinds of campaigns impact directly on the kind of violence that we see."

Bouckaert said the "ultimate intent" of Myanmar's military is to "completely cleanse Burma of the Rohingya population".

"They're not recognised as citizens in their own country, and they're not even recognised as refugees when they flee this brutality. So it's hard to think of a more abandoned people in the world. It's their very identity which is being destroyed."

Mental health implications of sexual violence

Kate White, emergency medical coordinator for Doctors Without Borders (MSF), which has on-the-ground clinics in Bangladesh's Rohingya refugee camps, said the sexual violence "is definitely widespread".

Since August 25, MSF had treated at least 23 cases of sexual and gender-based violence. Their services include medical care for physical injuries, sexually transmitted infection prophylactics and menstrual regulation for those who suspect they are pregnant.

Understanding just how widespread this violence has been, said White, is a challenge as those who are willing to come forward and seek care represent "the tip of the iceberg".

In the current crisis, where people are more vulnerable because of broken families and support structures and more households are now headed by women, White said people are forced to choose between collecting food or seeking healthcare. "Right now their priority is survival," she said.

White anticipates the long-term impact of the sexual violence will be on mental health. Many survivors MSF has treated are traumatised after being raped by multiple perpetrators or on multiple occasions while fleeing, said White, who spoke at MSF's Cox's Bazar office.

"I must admit this is some of the worst mental health outcomes that I've seen in terms of sexual violence. In terms of the impact that it's having on them - it's extreme," she said, describing how some survivors are unable to function on a daily basis.

The cultural stigma and shame associated with rape in Rohingya society mean many survivors are unlikely to speak about their experiences, let alone seek help, particularly unmarried girls who fear of being rejected by potential husbands.

Rajuma, the Tula Toli survivor, said her husband knows her story and stands by her. "He gives me the love he used to give," she said.

Yasmine's story: 'I thought I was dying'

In the newer refugee settlement of Palong Khali, further away from the food aid distribution and with few medical care outposts, along slippery mud tracks and surrounded by bright green rice paddies, lives Yasmine, whose name has been changed to protect her privacy. In an unfamiliar place, she said she is too ashamed to speak to anyone about what happened to her.

But she agreed to tell her story after her husband gave his consent.

The 45-year-old comes from Chawprang village in Buthidaung township. She arrived in Bangladesh with her husband and 11 children 19 days ago. The slender woman with a dusty yellow shawl draped over her head and her eyes wet with tears, described how, before the Myanmar army attacked her village, her family had grazed cattle and cultivated rice. Her children sold vegetables, betel leaves and river fish at the market.

"We were leading a good life before this crisis," said Yasmine, whose youngest child is four and eldest 26.

She doesn't remember the exact day troops attacked her village, but in the days leading up to it soldiers, beat villagers and stole their livestock, she said. Then they came one day at noon while she was feeding her three youngest children.

"They declared that you have weapons, surrender your weapons. If the villagers said that they had no weapons, then they started to kill them, started to torture them, started to beat them," she recalled.

Eight soldiers entered her house. They kicked and punched her children aged four, six and eight.

She covers her mouth with her shawl, looks down and speaks in a low voice. When the children were taken out of the house, she said five soldiers of different ages raped her while three waited outside.

"I'm not able to express this completely," she said through tears.

Her youngest child, a girl, wandered over, sat quietly next to her mother, and put her hand on her lap.

"I thought that I was dying," she said. The family fled several days later and paid a boatman to take them across the Naf River to Bangladesh.

"In Myanmar, I can't sleep properly. There is safety in my life, so I feel better here," she said.

'We want justice'

Back in Balukhali camp, Ayesha recounted how after she crossed the Naf River she set about looking for her husband, Asadullah, 25, who was a teacher at an Islamic school in Myanmar. He fled soon after August 25 when soldiers rounded up men from their village, murdered and tortured them. They beat him so badly that his leg is now deformed.

When she arrived in Bangladesh, she saw some villagers she knew and asked them if they had seen her husband. "Then one told another, one told another," she said. "This is how, after three days, I found my husband."

Asadullah said he is filled with anger. "I feel bad inside. I can't do anything to them," he said, adding he believes what happened to them was fate. "That's why I don't complain about what happened to my wife. I love her."

Ayesha said she has "pain inside my heart". For this reason, she added, "I tell this thing that happened to me, to reduce the pain, I speak about it."

In the cramped space, Ayesha spoke frankly, her eyes shining. "We want justice. What I want the people around the world to know is: we want justice," she said.

On the other side of the bamboo and plastic-sheet wall, a woman's voice called out: "We want justice."