Pope Francis visited a fortress prison holding mafia turncoats today and again included a Muslim and women in a traditional Holy Week foot-washing ritual that previous popes had limited to Catholic men.

Francis said a Mass for the 70 inmates of the prison, a 16th century fortress at Paliano 75 km (47 miles) south of Rome.

During the service, he bent to wash and kiss the right foot of 12 inmates, commemorating Jesus' gesture of humility towards his 12 apostles on the night before he died.

The high-security prison is reserved almost entirely for prisoners known in Italy as "collaborators of justice," those who turn state's evidence to testify against their former comrades and need special protection.

During the 1980s and 1990s it held turncoats from the Red Brigades guerrilla group but now most "collaborators of justice" are former members of Italy's three notorious organised crime groups - the Cosa Nostra, the Camorra and the 'Ndrangheta.

The Vatican said the 12 included three women and a Muslim man who has decided to convert to Catholicism and is due to be baptised in June. The 12 included 10 Italians, an Albanian and a prisoner from the pope's native Argentina who had written to him.

His predecessors held the Holy Thursday Mass in majestic settings either at the Vatican or a Rome basilica. Francis changed the tradition after he was elected to stress the importance of going out to serve the poor, the sick and the imprisoned.

The change drew the ire of traditionalists because all of apostles were male followers of Jesus, but the pope said the ritual should be open to "all members of the people of God".

The visit was private because most of the inmates could not be filmed or photographed.

"We are all sinners. We all have defects," the pope told the inmates in an improvised sermon broadcast by Vatican Radio.

By washing their feet, Francis told them, he was willing to do "the work of a slave in order to sow love among us". He urged them to help each other.

Two of the 12 are serving life sentences and the others are due to be released between 2019 and 2073.

Francis has condemned organised crime groups, saying their members indulge in the "the adoration of evil". He has said members of organised crime excommunicate themselves from the Church by their actions but could return if they repented.