Gardai have arrested a suspected IS extremist in Dublin who had been under surveillance after he was deported here from Turkey last week.
The suspect was sent back to Ireland after landing in Istanbul because of "irregularities" noticed on his passport by the authorities. He flew from Dublin to Turkey last Thursday.
Turkey has been used as a transit point to bring thousands of fighters from Europe, including dozens from Ireland, to the civil war in Syria.
Sources have revealed that on his return to the capital on Friday, it was decided not to arrest the man, who is aged in his 30s, in Dublin Airport but instead to put him under detailed surveillance over the weekend.
A decision was taken to arrest the man on Monday and his Dublin home was raided. He was brought to a city centre garda station for questioning about the eastern European passport which he had been travelling with, and which has now been seized.
He was questioned by anti-terrorist officers from the Special Detective Unit before being released without charge.
An "overt and covert surveillance" is expected to continue on the suspect, according to sources. A file will now be prepared for the DPP but gardai did not find any terrorist material connected to the suspect, who is understood to be an IS sympathiser.
Speaking earlier this week, Garda Commissioner Noirin O'Sullivan warned that attacks like last month's massacre in Tunisia, in which three Irish people were murdered, can happen "anywhere, any time".
"From an Irish perspective, when we hear of victims of a barbaric terrorist attack on a beach in Tunisia with Irish names and addresses, and the outpouring of sympathies at the funeral, it just brings it into sharp focus that anybody can be a victim, any time, any place.
"Ireland has a history of having to deal with its 'indigenous terrorist threat' but we must also be aware of new challenges," the commissioner said.
"We're very mindful that while we don't have any significant intelligence of an attack here in Ireland, nevertheless we remain very, very mindful and have a shared interest with our partners right across the globe."