A 45-year-old Dublin man has been arrested by Syrian Democratic Forces fighting ISIS in Syria.
He was one of five men detained, when patrols targeted a terror cell at Deir ez-Zor, on December 30.
The Kurdish backed Syrian Democratic Forces or SDF say it made the arrests after breaking up a terror ring that was preparing to attack civilians fleeing the war zone in masses.
The US supported militia says it detained five men, including one from Ireland, two from America and two from Pakistan.
The Irish passport holder is a 45-year-old man, who previously lived and worked as a security guard in Dublin.
The raid was carried out at Deir ez-Zor - the largest city in eastern Syria and the seventh largest in the country.
The Department of Foreign Affairs says it is investigating the circumstances surrounding the arrests and the identity of the passport holder.
Gardaí say the identity may be that of a naturalised Irish citizen who departed Ireland in 2013 and they are continuing to monitor developments.
The Taoiseach says he is aware of the reports and speaking during his visit to Mali in West Africa, Leo Varadkar said he is being kept informed of the situation.
"I've only heard about that in the last short while. The only information we have is that is that an Irish passport holder, an Irish citizen, has been taken into custody - is being held in Syria," said Mr Varadkar.
"We don't know the details of that so I can't comment on it in any detail.
"But what I will say is any Irish citizen around the world is entitled to consular assistance and we will get that."
In its statement, the SDF said: "The operation Jazeera Storm, carried out with the aim of liberating the last regions under the occupation of ISIS, continues steadily towards clearing the last bastions of the group.
"ISIS, which is now cornered in a small area after being cleared from large swathes of territory it once held, is suffering heavy losses due to operations of our forces.
"Recently, in order to prevent the advance of our forces, terrorists have attempted to carry out attacks several times.
"In this context, a group of terrorists who had been preparing to attack the civilians who were trying to get out of the war zone in masses was detected.
"Following long-term technical and physical follow-up, an operation against the cell was carried out by our forces.
"As a result of the operation, five terrorists originally from the United States, Ireland and Pakistan were captured."
