Pope Francis: Modern slavery is 'becoming worse and worse every day'

(CNN) -- Pope Francis said on Tuesday that modern slavery is a "crime against humanity" and is "unfortunately becoming worse and worse every day."

"This takes place in hiding, behind closed doors, in private homes, in the streets, in the cars, in factories, in the fields, in fishing boats, and in so many other places," the Pope said through an interpreter during a panel discussion Tuesday led by CNN's Christiane Amanpour. "This takes place both in cities and in villages -- in villages of the richest and the poorest nations on earth."

A diverse group of faith leaders gathered at the Vatican on Tuesday to sign a declaration pledging to "inspire spiritual and practical action by all global faiths and people of good will everywhere" to eradicate slavery by the year 2020.

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Photos: Pope Francis

Leaders and representatives of Catholic, Anglican and Orthodox Christianity, Judaism, Shiite and Sunni Islam, Buddhism and Hinduism all were present and signed the initiative.

CNN has championed the cause of eradicating slavery, having launched its Freedom Project in March 2011.

An estimated 35.8 million people are enslaved, according to the Global Slavery Index. As the Pope pointed out, the problem is far from limited to developing countries: More than 60,000 people are estimated to be enslaved in the United States, more than 10,000 in Germany and more than 1,000 in Sweden.

Most victims in Europe and Central Asia are forced into sexual exploitation, the United Nations says; in East Asia and the Pacific region, most are used for forced labor.

"The victims come from all walks of life, but most times they are the poorest and the most vulnerable of our brothers and sisters," Francis said.

The joint declaration calls modern slavery a "crime against humanity," and says that eradication in less than a decade is achievable.

"Today we have the opportunity, awareness, wisdom, innovation and technology to achieve this human and moral imperative," it states