More than €64m has been laundered through Ireland by international crime gangs, such as the 'Black Axe' organisation, according to gardaí.
The Black Axe is involved in transnational frauds, such as business invoice and romance fraud.
The Garda National Economic Crime Bureau said it has identified more than 800 so-called money mules, but estimates there are over 4,000 in Ireland.
Many of them have been recruited abroad and flown to Ireland to open accounts to launder millions.
A total of 264 people have been arrested for organised crime offences and money laundering, while more than 130 have been charged.
They have also warned people not to become money mules, as they risk a conviction under fraud money laundering and terrorist financing legislation in Ireland, which will limit their opportunities for work, travel and employment.
Gardaí are also part of an international operation involving Europol and international law enforcement agencies targeting the so called Black Axe criminal organisation, which is based in west Africa.
This investigation began two years ago with a request for assistance from an EU country after €1.1m was stolen in a BEC fraud and laundered through Asia.
The fake emails originated in Ireland and indicated that for the first time, the Black Axe criminal organisation was operating in Ireland.
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So far, the garda investigation has established that more than €40m has been stolen, with more than €64m laundered through Ireland via money mules.
Operation Skein was set up to target romance, business invoice and other fraudster operations in Ireland and has so far resulted in 69 people arrested under organised crime legislation and 195 detained for money laundering offences. A total of 135 of them have been charged.
Gardaí and Interpol are focussed on the activities of the Black Axe organised crime group, which has a global footprint.
They said it is involved in online fraud, human trafficking, drugs and gun crime, as well as murder.
Rory Corcoran, the Director of Interpol's Financial and Organised Crime Unit, said it was a sophisticated organisation with a business model that involves a division of labour.
Members and associates open bank accounts using false documents in one country, the crime is committed, money is stolen and victims are left in another country while the money is laundered in other countries.
Detective Superintendent Michael Cryan of the Garda National Economic Crime Bureau said that the gang’s method of operation keeps changing.
Prior to Covid-19, he said, a lot of criminals were flying into Ireland to open bank accounts. However, during the pandemic, they went online and recruited money mules to open bank accounts in their bedroom.
He added that they are starting to see Irish residents travelling to other countries.
Gardaí say the Black Axe organisation has sent people to Ireland and some have been convicted and jail.
They have laundered money, set up front businesses, used false documents and have been in direct contract with the leadership in west Africa.
Interpol said that while they have intercepted over $60m, they only recover 1% of funds, calling it "a bad track record which we need to improve".
Gardaí are also warning people not to agree to become money mules.
Detective Supt Cryan said: "If you’re a money mule, when you hand over your bank account, it will be used for organised crime.
"You’re the one that will be arrested, it’s your phone number, account, face on CCTV at the ATM."
He added that the way to tackle the fraud is to stop the money mules and cut off the gangs financial "blood supply".
