AUDIO: 'Abu Omar' was forced to fight with the IS in Syria for months
It is estimated that some 40 Irish men have gone to fight for ISIS in Syria and Iraq.
It is thought many of them joined the group, having been recruited from Europe.
It comes as figures show more than three times as many Irish Muslims have been to Syria compared to British Muslims.
One in every 1,500 Irish Muslims have travelled to Syria. In the UK, it is more like one in every 5,000.
Newstalk's Shona Murray is on the Turkish-Syria border.
She spoke exclusively to 'Abu Omar' - not his real name - who was a group leader of the Free Syrian Army.
He was forced to fight with ISIS from July, after the Islamic State took over his town.
But he defected and escaped from Syria into Turkey just a few weeks ago.