Pope Francis has appealed for forgiveness for all Christians who buy sex from women, describing it as torture.

During a four-hour listening session with 300 young people on what children think about the Catholic Church the 81-year-old pontiff was asked by Blessing Okoedion, from Nigeria, how Catholics could buy sex from Nigerian women trafficked into Italy as sex slaves.

Okoedion was forced into prostitution but managed to escape and attended the session designed to help Catholic leaders understand how young people view the Church.

'I ask myself, and I ask you: Is the male chauvinistic church able to truthfully ask itself about this high demand by clients?' she asked.

In response Francis said men who use prostitutes were criminals and had a 'sick mentality'.

'This isn't making love. This is torturing a woman. Let's not confuse the terms,' he said.

'This is one of the battles that I ask you young people to do, for the dignity of women,' he added.

Pope Francis told her: 'I want to take advantage of this moment, because you talked about baptised and Christians, to ask your forgiveness, from society and all the Catholics who do this criminal act.'