A top-ranking garda has said the threat posed by the so-called Islamic State (IS) terrorist group is "one of the biggest challenges in the 200-year history of law enforcement in the western world".
Assistant Commissioner John O'Mahoney, head of the Garda Crime and Security Branch, said up to 40 individuals had travelled from Ireland to fight in the Middle East since 2010, including some who joined Isil.
He said the Isil is "an unprecedented global phenomenon which does not respect national borders and utilises the digital age . . . to radicalise and recruit people and incite terrorist acts".
Mr O'Mahoney said officers from the Counter Terrorism International (CTI) unit had contacted individuals intent on leaving Ireland to fight in Syria and Iraq after being tipped off by their families or friends.
"The CTI actively engages with people who are planning on travelling to those war zones in order to discourage them from doing so," he said.
He said officers also engage with people returning from the war zones "with a view to assessing the threat they pose based on their beliefs and activities", though he could not reveal the numbers involved for "security reasons".
Mr O'Mahoney said gardai had been successful in fighting domestic terrorism for almost 50 years.
"As a result, we have a formidable skills base in this field, which means we are well able to face this challenge," he said.
"But it is important to stress that while the threat assessment is that an attack is possible, it is unlikely."
The security services have drafted strategic and operational plans to deal with Paris-style terror attacks.
Mr O'Mahoney said such attacks had been re-created in elaborate training exercises played out in what he described as table-top drills designed to test the responses of the gardai, Army and emergency services.
He also said gardai and Justice Department officials have been travelling to Jordan, Lebanon and Greece to vet refugees coming to Ireland in a bid to weed out Isil fighters hiding among them.
He said it would be "naive" believe Isil would not seek to use the mass movement of people to its benefit.
However, he added that it is "important not to conflate the refugee crisis with the terrorist threat", saying the "vast major- ity" of people fleeing the Middle East have genuine reasons for leaving.