Pope Francis surprises 20 former prostitutes by knocking on their door in Rome and popping in for a chat

Pope Francis surprised 20 former prostitutes on Friday by knocking on their door in Rome and popping in for a chat.

The Argentine, who has repeatedly described the human trafficking behind much prostitution as 'a crime against humanity', sat down with the group, including four women from Albania, seven from Nigeria and six from Romania.

The other three women - who are being sheltered by a Catholic charity in an apartment - hailed from Italy, Tunisia and the Ukraine. 

The women, all aged around 30, are being sheltered by a Catholic association in an apartment in the Italian capital after being rescued from their pimps.

The 79-year old listened for over an hour to the stories of the former sex slaves, 'all of whom suffered serious physical abuse and live under protection,' the Vatican said.

The visit fell under what have been termed Francis's 'Fridays of Mercy', whereby he carries out one unscheduled act of mercy a month on a Friday. 

These take place mainly in or near Rome throughout the pope's Jubilee year, which started in December and runs to November.