Detectives investigating a bomb in a van left on the A1 last week have carried out a number of searches in Newry, Warrenpoint and Rostrevor.
Searches were also carried out in Belfast.
No arrests have been made, but a number of items were removed for examination.
A 26-year-old man arrested earlier on Thursday in connection with the bomb remains in custody.
The man was arrested in the Rostrevor area and is being questioned in Antrim.
The 500lb bomb was discovered in a van abandoned on the Newry bypass last Thursday.
Hundreds of motorists drove past the vehicle after cones cordoning it off were removed.
Army bomb experts carried out several controlled explosions on the vehicle.