Two men have been arrested under Section 30 of the Offences against the State Act in Co Louth and Monaghan today.
The men were detained in the Tallinstown and Inniskeen areas, shortly after 8am this morning.
They are being held at Carrickmacross Garda station in Co Monaghan.
It is understood the two, aged 24 and 28, are being questioned about membership of an illegal organisation.