Two women and two men have been arrested by detectives from the PSNI Terrorism Investigation Unit investigating violent dissident republican activity.
The arrests follow searches in counties Tyrone and Armagh this morning (Wednesday).
Properties in Drumquin, Benburb and Armagh were searched and a number of items have been seized.
The two women, aged 31 and 23, and two men, 55 and 30, are being questioned at the Serious Crime Suite at Musgrave Police Station in Belfast.