Searches are being carried out in Northern Ireland by detectives investigating dissident republican activity.
The PSNI say the searches, into the activities of "violent dissident republican terrorists", are taking place in Strabane.
The operations are in connection with a number of recent incidents across Derry city and Strabane.
Police say these incident include pipe bomb attacks across Strabane in July and earlier this month.
Detective Inspector Michael Winters said: "We are committed to disrupting the activities of these groups.
"We know that the vast majority of people support us in our aims and will continue to stand with us as we work to dismantle these groups and free communities from the threat they pose."