Updated

Pope Francis has met with four women who were forced into prostitution as he denounced human trafficking as a crime against humanity.

Francis left the Vatican on Thursday to attend a conference of church workers, charity representatives and police chiefs from 20 nations who pledged greater cooperation to encourage victims of trafficking and slavery to come forward.

Francis told the conference that trafficking is "an open wound on the body of contemporary society." He met privately with four freed sex slaves from his native Argentina, Chile, Hungary and the Czech Republic.

Francis has made human trafficking and slavery a priority of his papacy.

The Vatican recently joined forces with the Anglican Church and Al-Azhar university, the world's foremost seat of Sunni learning, in an anti-slavery initiative.