Two men, aged 29 and 34, have been arrested in Belfast, and a further nine in Romania, in a joint operation targeting the alleged trafficking of young women for prostitution, according to the PSNI and Eurojust, the EU agency for police cooperation.
"This operation was set up specifically to disrupt and dismantle Romanian organised crime groups who are working in Northern Ireland and Romania," the PSNI said in a statement.
Eurojust said the gang used the so-called "lover-boy method", whereby men lure female victims into prostitution through the promise of sentimental attachments and future financial earnings.
"During a joint-action day, nine suspects were arrested in Romania and two in Northern Ireland," Eurojust said.
"Female victims who were sexually exploited have also been identified and their rights and safety will be ensured."
Eurojust said 15 properties were searched in Romania and Northern Ireland, with ten luxury cars, as well as jewellery and cash, seized.
"The seizures are deemed to be part of the profits of the organised crime group (OCG) pretending to be interested in relationships with women in vulnerable positions due to their age and/or personal or financial situations, but in reality forcing them into prostitution in the UK," the statement said.
"These so-called 'lover boys' promised financial contributions to the victims’ families, but kept all profits of the sexual exploitation for themselves."
Eurojust said most of the profits were invested in real estate and luxury vehicles in Romania.
The operation was carried out by various Romanian law enforcement agencies, and was supported by the Public Prosecution Service for Northern Ireland and the Police Service of Northern Ireland, with officers present on the ground in Romania.
Last September, a similar investigation centred on the "lover-boy" trafficking of young women into Ireland, the UK and Germany.
Detective Inspector Gina Quinn from the PSNI's Modern Slavery and Human Trafficking Unit said: "The Organised Crime Group targeted today is believed to be responsible for recruiting and trafficking people from Romania into Northern Ireland for prostitution and money laundering.
She added: "This operation, which also included two officers from the Police Service of Northern Ireland assisting police in Romania, has been made possible through a Joint Investigation Team (JIT) agreement between the UK and Romania.
"Eurojust, the EU agency set up to promote co-ordination between member states in relation to serious and organised crime, has partly funded the operation. The operation was assisted and supported by Europol and the Police Service of Northern Ireland, the Public Prosecution Service in Northern Ireland and the Service for Countering Organised Crime (SCCO) Romania."
Detective Inspector Quinn said: "Working with law enforcement colleagues we believe we may have halted the activities of an organised crime gang involved in controlling prostitution, human trafficking and money laundering in Northern Ireland and Romania.
"Crime groups choose to exploit some of the most vulnerable people within our societies, preying on their vulnerabilities and exploiting them for their own ends."