Detectives were questioning four dissident republican suspects today as part of an intelligence operation in the North.
As part of the police operation searches are also being carried out near a railway line in Co Armagh causing major disruption to the Belfast to Dublin train route.
The four men arrested were stopped in a car on the Antrim Road, Lurgan, last night.
They were taken for interview at the Police Service of Northern Ireland’s serious crime suite in Antrim.
As the operation continued, officers sealed off the railway line between Moira and Lurgan.
St Michael’s Grammar School in the town was also closed during the searches.
Cross-border train passengers were bussed between Belfast and Newry, Co Down.