In a statement police said the traffickers allegedly performed voodoo rituals on the women to make them swear to repay the cost of the trip to Europe, and warn them that their relatives would die if they did not.

“Once in Italy, criminals would help the women escape from migrant centres and take them to the north-western city of Turin, where they would be told that prostitution was the only way in which they could repay their debt.

“Some women were asked to pay as much as 30,000 euros (35,200 dollars),’’ the police said.

On July 22, the International Organisation for Migration (IOM) had issued a report saying that three-quarters of the roughly 11,000 Nigerian women who landed in Italy in 2016 may have been taken there by sex traffickers.

The IOM, a UN agency, said it was difficult to make precise estimates because most victims of the sex trade are afraid to speak up and seek assistance because of shame, submission to traffickers accompanying them on migrant boat, or fear of retaliation against their relatives.

In a separate incident in the Nuoro area, a local migrant centre was attacked overnight by a powerful makeshift bomb that destroyed one of its side entrances.

Two of the 64 migrants hosted there reported light injuries to their legs.

– NAN