Published Friday, 04 July 2014
Officers carried out searches in Londonderry on Thursday night as part of the investigation.
A house in Derry's Creggan is understood to have been at the centre of the probe.
The worried family of a man who has been missing for months, 25-year-old Eamon Bradley, told the Irish Mirror earlier this week that he had been in touch to tell them he had joined rebel forces.
Confirming the investigation, a PSNI spokesman said only: "Police are making enquiries into reports of a Northern Ireland man in Syria."
UTV North West reporter Gareth Wilkinson said the Bradley family had declined to be interviewed.
Warnings against travelling to the conflict-hit country have remained in place for some time now from both the Irish Department of Foreign Affairs and the British Foreign Office.
Dublin officials warn: "If you're planning a trip to Syria, we advise you not to travel. If you're currently in Syria, we strongly advise you to leave immediately while this is still possible.
"We cannot guarantee that the Honorary Consul of Ireland in Damascus will be able to remain open for much longer.
"Ireland has no embassy in Syria and, if the consulate has to close at short notice, it's extremely unlikely that we'll be able to provide any consular assistance to Irish citizens who decide to remain in Syria."
By all accounts, Eamon was a fairly normal guy here with an average up-bringing. But in recent years, he is said to have become increasingly interested in Islam and may well have converted.
Gareth Wilkinson, UTV
Officials in London also advise against all travel to Syria, adding: "British nationals in Syria should leave now by any practical means. The FCO (Foreign and Commonwealth Office) is not able to provide consular services, and won't be able to help your evacuation from the country."
It comes as religious leaders across the UK urged British Muslims not to travel to Syria or Iraq to join the conflict.
A number of British men have appeared in recent propaganda material issued by the insurgent group Islamic State in Iraq and Greater Syria (ISIS).
But an open letter from imams, during the Islamic festival of Ramadan, notes that it is the "month of mercy" and calls for British Muslims not to get involved with insurgents.
"We urge the British Muslim communities to continue the generous and tireless efforts to support all of those affected by the crisis in Syria and unfolding events in Iraq, but to do so from the UK in a safe and responsible way," they write.
Earlier this year, the Met Police called for people to come forward with information about family members if they feared they may join terrorist training camps in Syria.
The US Department of Homeland Security has stepped up security, including at international airports operating direct flights to the country, in the wake of what has been called "a credible threat".
Two terror networks are suspected to be working on a bomb plot aimed at sidestepping existing security checks.
© UTV News