Two men are being questioned in Drogheda Garda Station about dissident republican activity.
The two men were arrested in the Dundalk area this morning.
They are being held under Section 30 of the Offences against the State Act.
Elsewhere, the PSNI also arrested two men in connection with dissident republican activity.
One man was arrested in Derry this morning following two house searches.
He is being questioned in the serious crime suite at Antrim police station.
A second man, who was detained in the Strabane area, is also being questioned in Antrim.