Highly organised Nigerian gangs are earning “extremely high profits” from trafficking children into 12 European countries, including Ireland, for prostitution, according to the EU police agency.

Europol said victims generate a smuggling debt of between €30,000-€60,000 each — and that paying off the debts can take years.

The agency said Nigerian criminal groups are organised into cells, typically run by females, known as “madams”, with men working in supportive roles.

The Europol report on the trafficking and exploitation of underage victims said southern EU countries, such as Italy and Spain, are the main entry points for trafficked Nigerians.

It said victims are then forced into prostitution in both the two entry countries and 10 other member states, including Ireland.

It said Nigerian organised crime gangs pose a “great challenge” to EU law enforcement. It said they were well organised, but not structured like most other crime networks.

“The typical Nigerian criminal group is not hierarchically structured but rather organised into cells, among which female suspects usually execute the core business [recruitment and exploitation], with male members having supportive roles,” said the report.

“Contrary to other criminal groups involved in human trafficking, where female members are generally employed as victim controllers, the figure of the ‘madam’, including acting as a ring leader, is central for the Nigerian THB [trafficking of human beings] business.”

The report said the cellular structure makes it easy to move victims and that if one cell is dismantled by police, the other cells can continue operating.

It said: “Nigerian networks generate extremely high criminal profits, as each victim is forced to pay back the organisation usually between €30,000 and €60,000.”

It said most victims of Nigerian gangs were aged between 15 and 17, though the reports documents children aged 11-15 and some aged six-10 and even under five.

The girls were often promised well-paid jobs. The gangs often involved family relatives to persuade the girls to move and in other cases use voodoo rituals.

It said victims are passed from trafficker to trafficker and are “frequently subjected to physical assaults” and subsequently sexually exploited.