The focus of the investigation will be the suspect’s links to Syria and other middle-eastern countries.
Armed members of the Special Detective Unit (SDU) were involved in the planned operation which led to the suspect aged in his early 40s being brought to Castlebar Garda Station for questioning on Monday.
He was later released without charge and detailed investigations into his alleged activities are ongoing with a file being prepared for the Director of Public Prosecutions (DPP).
The suspect is originally from a middle Eastern country but has lived in Ireland for a number of years where he is involved in running a business in a Co Mayo town.
Sources say that he was previously investigated by authorities here in relation to the smuggling and sale of cigarettes but he has no criminal convictions.
A main focus of the investigation will be the suspect’s links to Syria and other middle eastern countries.
“Information has come in that this suspect has been sending money out of the country to the Middle East which is one cause of huge concern,” a senior source said.
“Another major cause of concern is how and why he had such a large amount of cash when gardai carried out the raid.
“This individual has certainly under-the-radar in terms of involvement in general crime but his arrest and the cash seizure are very significant and highly unusual.
“The arrest and search operation were carried out in a very discreet fashion as this is a sensitive case,” the source added.
Arrests for terrorist financing are relatively rare in Ireland with only four arrests of jihadist terror suspects being made in the country last year.
The EU Terrorism Situation and Trend Report (TE-SAT) produced by Europol was published last month and the report gave no details of the four Jihadist terrorism suspects who were arrested in Ireland in 2021.
There was one right-wing terror suspect arrested, seven dissident republican or loyalist suspects and two which were not specified in the data given to Europol.
It is unclear whether this week’s arrest in Co Mayo is the first this year by gardai investigating international Jihadi terror groups which are carried out in top secret.
In 2020, gardai arrested 18 men and women in Ireland for this type of offence.
The majority of the Irish based suspects were detained on suspicion of fundraising for terror organisations by sending money to countries including Turkey, Afghanistan, Iraq and Syria.
Those arrested included Irish citizens, foreign nationals, and people with dual citizenship.
In the five-year period between 2017 and 2021 there were 30 arrests of people in relation to Islamic extremism. In five years before that there had been just one.
Several anti-terrorist investigations are ongoing by the SDU which target lone individuals and groups that include men and women with Irish nationality, dual nationalities, and foreign nationalities.
Sources say that prosecutions for financing terrorism are rare because of the difficulty in proving that a donation to a person or entity is for the purpose of supporting terrorism.
However what makes this week’s seizure in Co Mayo different than many other Irish cases is the very large amount of money that was seized by gardai.
Former soldier turned Islamic State( ISIS) member Lisa Smith (40) who is serving a 15 month sentence for being a member of the group was found not guilty of financing terrorism by sending money to a man for the benefit of the group at her trial in the Special Criminal Court.
The Dundalk woman was acquitted of a charge of financing terrorism by sending money to a man in May 2015 for the benefit of ISIS.
She denied sending €800 via a Western Union money transfer to a man in May 2015, knowing or intending it would be used for the benefit of ISIS.