Zunera once dreamed of becoming a computer engineer. Instead, aged 16, she was tricked into prostitution in the UAE, beginning a four-year nightmare of cruelty, violence and rape.

Pakistan has long been an important source of cheap labour for the Gulf state, particularly its booming construction sector.

But campaigners and officials say hundreds of young Pakistani women are also trafficked every year to supply the thriving sex trade in the brothels and nightclubs of Dubai. Zunera and her sister Shaista were two of them.

More than a year after she escaped, Zunera's pain is still etched into her stumbling, hesitant voice -- and also into her body, which bears the marks of countless beatings.

Vivid, angry scars run the length of her legs from ankle to hip, reminders of a botched operation after she was shot three times by the gang who trafficked her.

Zunera and Shaista managed to escape their tormentors in 2013 but still live in hiding in a two-room house in a slum, fearing revenge attacks. AFP is withholding their full names and precise whereabouts for their safety.

Their ordeal began in her hometown in Punjab province, when the family got into money trouble and a neighbour named Ayesha offered the sisters domestic work.

After a while Ayesha suggested she take the sisters to Dubai to work in her beauty parlour, getting fake papers to help the underage Zunera leave Pakistan.

Shaista is so traumatised by her experiences she can barely recount her harrowing ordeal.

Fighting back tears, Zunera revealed the horror that awaited them at Dubai.

"Ayesha took us to the lavatories at the airport and told us that we will be serving her clients for sex," Zunera told AFP.

"We started crying and then she told us that we travelled on fake documents and if we said anything we would be handed over to police right there."

Faced with no alternative, the sisters went with Ayesha, thinking they could just avoid having sex with clients.

"The first time, she herself was present in the room and made us do what the clients wanted. We were raped in front of her and with her assistance," Zunera said.

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- Escape, but little freedom -

"She used to beat one of us and ask the other sister to talk on phone to our parents, threatening to kill us if we revealed anything about the brothel," Zunera recalled.

From time to time Ayesha brought the women back to Pakistan to renew their visas, frightening them into silence by telling them she would kill their whole families if they revealed the life they had been tricked into.

But eventually in March 2013 the sisters plucked up the courage to share their ordeal to their elder sister Qamar, who eventually obtained their freedom -- but at a cost.

"The brother of Ayesha and the younger brother of her husband came to our house. They fired three shots which hit me," Zunera said.

After that, Ayesha told the clients to keep their cell phones connected to her number during the intercourse so she could hear what was happening -- and if they were refusing to cooperate.

"She used to torture us whenever we refused to perform certain sexual acts, and she told us that she knew whatever had happened inside the bedroom," Zunera said.

The women were not allowed to go out or even speak to one another freely. They could speak to their family in Pakistan by phone occasionally, but under duress.

"In hospital, she sent policemen who harassed me and asked me to start walking despite the fact that my leg had undergone surgery."

The family fled from the hospital and went into hiding because their neighbours also started abusing them for being "prostitutes".

Zunera's family approached a court to try to crack trafficking ring run by Ayesha and her husband Ashfaq. The court ordered the Federal Investigation Agency (FIA) to act but the case has since made little progress.

Lawyer Zulfiqar Ali Bhutta, who is fighting Zunera's case, says the trafficking gangs often have influential connections to politicians and the police.

"Several gangs smuggle dozens of young girls from Pakistan to Dubai for prostitution every week. Nobody takes action against them," Bhutta said.

"The main accused in this case, Ashfaq, fled from the court in front of FIA officials. They did not arrest him despite the court cancelling his bail," he said.

A recent US State Department report on people smuggling said the UAE government was making significant efforts to tackle sex trafficking, pointing to prosecutions and protection offered to victims.

In 2013, the US report said, the UAE government identified 40 victims and referred them to state-funded shelters.

But if the UAE authorities are keen to confront the problem, in Pakistan indifference reigns.

"It is true that hundreds of girls are being taken to Dubai for work in beauty parlours, in music and dance troupes, but there is no proof that any of them has been smuggled for prostitution," Syed Shahid Hassan, deputy director FIA Faisalabad, told AFP.

For Zunera and Shaista, their ordeal has abated but not ended.

Ayesha has surrendered to a court but been freed on bail. The sisters now live in constant fear that a gunman will come back for them.