A suspect is being questioned in Lebanon over the death of Private Seán Rooney.
The Irish soldier was shot and killed when a United Nations convoy he was travelling in came under attack on December 14th.
The AFP news agency reports that the 'prime suspect' was handed over to Lebanese authorities by the militant group Hezbollah.
Hezbollah has denied any involvement in the shooting, and it is not clear whether the suspect is a member of the militant group.
There is no official confirmation of any arrest from the Lebanese government or armed forces.
The Defence Forces has said it will not be commenting on the reports.
Private Rooney joined the Defence Forces in March 2019. He previously served overseas with the 119 Infantry Battalion UNIFIL.
The native of Newtowncunningham, Co Donegal was laid to rest with full military honours last week.
Private Shane Kearney, who was injured in the same attack, is receiving treatment in Dublin after being medically evacuated from Beirut.
The incident in Lebanon is under investigation by Irish authorities, UNIFIL and the Lebanese Armed Forces.
Ireland has lost 48 soldiers serving for peace in UNIFIL, the most of any contingent.