Three men and a woman are currently being detained under Section 30 of the Offences Against the State Act
Four people have been arrested in connection with the robbery of a post office earlier this year.
Three men, one in possession of a firearm, entered the Post Office at Clogherhead in county Louth on the May 3rd 2016.
Staff were threatened and the robbers fled the scene with a large amount of cash.
Gardaí investigating the robbery arrested four people this morning in the Louth area in connection with the incident.
Three men, aged 30, 33 and 42, and a woman (23) are currently being detained at Balbriggan, Dundalk, Drogheda and Navan Garda Stations.
A number of premises were searched this morning in the Drogheda District in connection with this investigation.