Two men were arrested during a two-day operation into criminality linked to the New IRA in Strabane on Monday.
Detectives from the PSNI's Terrorism Investigation Unit also conducted six searches in the area during the operation.
Detective Chief Inspector Andrew Hamlin explained that the men - aged 26 and 34 - were arrested in connection with recent attempted paramilitary-style attacks and a weapons find in the Strabane area in March.
The men are currently being questioned.
"Detectives also searched five houses in Strabane during which they recovered a number of items which were removed for further examination," continued Detective Hamlin.
"As part of the investigation into an improvised mortar device that was discovered in Church View, Strabane, in September 2019, detectives conducted a search of land in the greater Strabane area."