Three men were being questioned today in connection with a number of pipe bomb alerts in the Strabane area.
Two homes in Strabane and one in Sion Mills were searched by police in relation to recent dissident republican activity.
The men were today being interviewed at the serious crime suite at Antrim police station.
The arrests came after vulnerable adults were forced to evacuate a residential home and a daycare centre in Strabane after the latest pipe bomb scare yesterday.
Ten residents at Iona House and 15 from the Glenside Adult Care Centre were moved out of their Derry Road premises by staff after the alert began at 10.45am.
Workmen discovered a plastic barrel dug into the ground and a police officer at the scene later revealed that two devices were found inside a sealed plastic sewer pipe within the barrel.
Around 200 people working at the district council offices were sent home and two emergency response ambulances also had to be drafted in when paramedics stationed at the rear of the council building could not access their vehicles.
The find, described as a "transit hide" is the latest in a spate of similar incidents in the district.
Army technical officers were called to examine three other viable devices left in and around Strabane on Monday, Tuesday and on Wednesday, when a community bus to deliver meals on wheels was stolen and a device later found on board when it was recovered.
However Strabane Community Project, which lost the valuable bus, extended a hand of friendship to the evacuees from Iona House and Glenside on Thursday, inviting them to St Patrick's Hall at Barrack Street and offering shelter and a hot lunch.
Staff from Iona House and Glenside paid tribute to the Project for its help, adding that, due to contingency plans, elderly and vulnerable people were moved from their accommodation with minimum stress.
Thomas Kerrigan, chairman of Strabane District Council, hit out at those responsible for the spate of alerts.
"These items are indiscriminate and the people who left them are careless and unthinking," he said.
"I have to ask, whose agenda are these people working to?"