Italian and Dutch authorities on Tuesday arrested dozens of Nigerians accused of smuggling their compatriots, some as young as 15, into Europe to work as prostitutes and drug traffickers, police said.

The police operation also uncovered that it called "serious adoption irregularities" in which Nigerian women living in Italy were apparently able to take infants from Nigerian orphanages and then sell them abroad, a police statement said.

Officials offered few details at a news conference, saying that they knew of only one case in which two children were taken from an orphanage and handed over to a prostitution "madam" in Italy. But officials said they believed it was a growing trade and that one aspect of the investigation would now focus on contacting Nigerian authorities to ensure that such illegal international adoptions end.

Overall, authorities carried out 66 arrest warrants early Tuesday, all but 15 of them in Italy.

Dutch authorities made most of the 15 other arrests. Smugglers in the Netherlands played an important role in getting Nigerians into the country, the statement said.

Most of those brought in were young, some as young as 15, and they were then sent elsewhere in Europe to work as prostitutes or in the drug trafficking industry, the police said

The suspects in Italy are accused of mafia association, criminal association aimed at human trafficking, slavery, kidnapping and international drug trafficking, police said.

Many of those arrested were prostitution madams, who pay thousands of dollars for each new girl to be smuggled into the country, said Giovanni Conzo, an anti-mafia prosecutor in Naples where the Nigerian operation carried out much of its work.

Other young Nigerians were used as drug mules, paid about $4,500 per trip to swallow cocaine or heroin in condoms and transport it around Europe, he said.

The investigation, which began in 2006 and has resulted in 150 arrests, also found that drug running in Europe had gone low-cost, a police statement said. The smugglers move around the continent on low-cost airlines, flying into secondary airports such as Bergamo in Italy or Karlsruhe in Germany, it said.

Interior Minister Giuliano Amato called the arrests proof that a new slave trade was growing in Europe, taking advantage of poor young Nigerians.