Two Tunisian policemen accused of raping a young woman in 2012 denied the charge on Monday, instead accusing the alleged victim of seeking to have sex with them.

"They denied everything," Radhia Nasraoui, the lawyer of the young woman known by the pseudonym Meriem Ben Mohamed, told AFP.

One of the accused claimed instead that the young woman had tried to perform oral sex, Nasraoui added.

Koutheir Bouallegue, another of the victim's lawyers, confirmed that the policemen denied raping her.

"One of them admitted that he masturbated," he said.

Journalists were barred from attending the closed session, which began mid-morning.

Three police officers are facing trial over the incident, which took place in September 2012, two of them accused of rape.

The defendants say they found the young woman and her boyfriend having sex in their car in a Tunis suburb.

According to the charges, they then took the woman to a police car, where two of them took turns to rape her, while the third policeman allegedly tried to extort money from her fiance at a bank cashpoint.

The public prosecutor tried unsuccessfully to bring indecency charges against the couple, sparking a storm of protest and a campaign of support for the young woman.

Speaking before Monday's hearing, Ben Mohamed said she was not optimistic about the outcome of the trial but voiced determination to see her aggressors brought to justice.

"If only this whole episode would finish. But I will not give up, whatever the verdict," the young woman told AFP, standing beside her boyfriend.

She has already published a book in France giving her account of what happened, entitled "Guilty of being raped."

Outside the court house, a small group of supporters waved banners and shouted slogans, including Amina Sboui, a former member of the radical women's protest group Femen.

"I'm here to support Meriem and all women victims of rape. Anyone guilty of raping a woman should be punished," Sboui said, urging victims to take legal action.