Pope Francis met with four former sex slaves on Thursday at a conference encouraged to fight human trafficking, FoxNews.com reported.

The two-day conference was attended by church workers, charity organizations, and police chiefs from 20 countries who are pledging to make a greater effort assisting victims of forced prostitution.

Francis met privately with former slaves from Argentina, Chile, Hungary, and the Czech Republic. He called human trafficking "an open wound on the body of contemporary society, a scourge upon the body of Christ. It is a crime against humanity."

Attendees included British Interior Minister Theresa May, Interpol Secretary-General Ronald Noble, and London Metropolitan Police Chief Sir Bernard Hogan-Howe, according to Reuters.

Hogan-Howe told reports that the work of church groups and law enforcement agencies is vital to ending sex slavery.

"This is a pretty powerful network. We have the heads of the various police forces (and) many people who are leaders. They are committed," he said. "Apart from its mere statement, it encourages governments to pass laws. By making such a declaration it encourages governments to take this to a very high priority."

The Vatican is already working with the Anglican Church and Al-Azhar University in an anti-slavery movement, according to Fox News.

The Walk Free Foundation reported that 30 million people are forced into sex slavery across the world. The men, women, and children are trafficked by gangs for sex work or unskilled labor.

"We learned that just one percent of people caught in human slavery are being rescued," said Cardinal Vincent Nichols, the Archbishop of Westminster. "The comment was made that slavery has never been as widespread in the world as it is today."

According to Reuters, Francis thought of hosting the second annual conference this year. When President Barack Obama visited the Vatican last month, he spoke with him about an international effort to end slavery as well.