More than 130 premises were raided and eight people arrested in a cross border operation targeting organised prostitution, criminality and money laundering.
Police in Northern Ireland rescued three suspected victims of human trafficking when they search 10 brothels across the region on Tuesday.
Five people were arrested as every county across the north, plus Belfast and Londonderry, were visited during Operation Quest.
At the same time detectives in the Irish Republic searched 114 apartments, flats and houses. One man and two woman were arrested for questioning.
A significant amount of documents, cash, mobile phones and computers were seized in both jurisdictions and are expected to result in several bank accounts being frozen.
Police Service of Northern Ireland (PSNI) Detective Superintendent Philip Marshall said: “We are determined to actually do something about this problem. It is not something society should stand for, it is a criminal offence and police do take it seriously.”
He said the operations demonstrated the commitment of the PSNI, Irish Garda and other law enforcement agencies across Europe.
Officers in Northern Ireland visited more than 20 addresses and searched several of them.
A PSNI spokesman said they believed 10 of these locations were being used for the purposes of prostitution. Five arrests were made for a variety of offences and three suspected victims of human trafficking were rescued, police added.
It involved 170 police officers across Northern Ireland and had been planned for several weeks.
Detectives received support from women’s help organisations who deal with rescued victims of trafficking and representatives of the Garda were in the Belfast command room. Women were taken to special suites at police stations for dealing with those trapped in the sex trade.
Police questioned one woman discovered at a flat in the city centre. A team of officers with specialist equipment including heavy duty lock breakers had mustered nearby and took mere seconds to break into the locked flat after a knock to the door went unanswered.
Three or four officers pushed the door open, rushed into the room shouting “police” and found the woman, of foreign appearance, inside. Police wearing rubber purple gloves conducted a thorough search and gathered evidence in a special plastic bag.
The woman was later led away for questioning, a black coat hiding her features from cameras.
Det Supt Marshall said officers were responding to concerns in wider society about sexual exploitation and human trafficking.
“Today’s operation is focused on getting information and evidence on the extent of the problem of organised prostitution in Ireland,” he added.
“We suspect there is a number of crime gangs involved in this.”
The probe was not focused particularly on paramilitaries.
An organisation that campaigns for ethnic minorities has said Northern Ireland has the fastest growing sex industry in any part of the UK.
The claim was made as Stormont Justice Minister David Ford announced plans for two new laws to combat human trafficking. Between April last year and February this year police identified 26 potential victims in Northern Ireland. The countries they come from include Ghana, Zimbabwe, China and Slovakia.
In February, a man was convicted for trafficking in a Northern Ireland court for the first time.