A steep rise in the number of Nigerian prostitutes working in Italy is being linked to the arrival in the country of well-organized Nigerian mafias, which are using violence and religious rites to terrify trafficked women into submission, police say.

Police say their operations this year have revealed the presence in Italy of a host of Nigerian gangs with names such as the Black Axe, the Vikings, the Buccaneers, the Eiye and the Maphites.

The gangs have arrived in Italy as the number of Nigerian women sailing to the country from Libya has risen from 1,454 in 2014 to 10,624 between January and the end of November.

Of those, as many as 80% are forced to work as prostitutes, according to the International Organization for Migration.

With prices for sex with girls as young as 14 starting at around $10, 1 in 2 street prostitutes in Italy today is Nigerian.

Seventeen members of the Black Axe mafia were arrested last month, including the group’s “head of zone” for Italy, taken into custody in Verona, and the “minister of defense” in Palermo. The latter was said to be responsible for singling out errant members for machete attacks.

“Our probe showed how gangs like the Black Axe are running the whole prostitution pipeline, which brings trafficked women from Nigeria to Italy,” said an investigator in Palermo who declined to be named because he was not allowed to speak on the record.

Women are usually fooled into believing they will be given regular jobs in Europe by traffickers who stage voodoo rites in which the women promise to pay back the cost of their travel, authorities said.

Upon arrival, police said, the women are told they must work as prostitutes until they pay off debts of about $30,000.