Four people are being questioned in connection with the suspected funding of IS groups in Syria.
The four – three women and one man – were arrested following six searches in Dublin conducted by the Special Detective Unit.
The arrests were made on foot of a major investigation by Garda intelligence and financial units.
Detectives suspect that the family-based group was sending funds through a bank to people in Syria who are suspected of being affiliated to the so-called Islamic State.
The intelligence part of the operation was conducted by the Terrorist Financing Intelligence Unit (TFIU), attached to the Garda National Economic Crime Bureau, and the Security and Intelligence Section at Garda Headquarters.
The investigative and arrest operation was conducted by the Special Detective Unit, which has a particular section, Counter-Terrorism International, dedicated to international terrorism.
Members of the TFIU were present during the search and arrest operation.
The operation has been described by security sources as “very significant”, but it has been stressed that more work has yet to be carried out.
A Garda statement said: “This morning, 22nd January 2019, as part of an ongoing investigation by the Special Detective Unit, The Garda National Economic Crime Bureau and Security & Intelligence into international terrorist financing, a series of six searches were conducted in Dublin."
It said: “Documents, electronic equipment and €4,500 cash was seized. Four persons were arrested for suspected terrorist financing contrary to Section 13 of the Criminal Justice (Terrorist Offences) Act, 2005 and are currently detained under Section 4 of the Criminal Justice Act, 1984 at Dublin Garda Stations.”
It added: “The arrested persons are a man in his 40s, three females, one in her 30s, one in her 40s and one in her 60s. The investigation is on-going.”