Police are searching a country park in the North as part of a terrorism investigation which prompted the arrest of a British Royal Marine.
Ciaran Maxwell, 30, from Larne, Co Antrim, was detained by Metropolitan Police officers in southern England in a planned swoop last week. He is still being questioned.
The investigation is linked to the discovery of two dissident-related arsenals in woodland in the North earlier this year.
Officers have returned to Carnfunnock Country Park near Larne, where they found bomb-making items in March.
Last Wednesday's arrest operation involved searches at a house and wooded area in south Devon, England. Searches at the property in Exminster and nearby Powderham New Plantation woods continued the following day.
Officers searched a number of properties in Larne last week and carried out fresh inquiries this week.
Maxwell is being detained on suspicion of preparation for acts of terrorism.
While the threat posed by violent dissident republicans in Northern Ireland has been classified as severe for a number of years, in May the UK intelligence services raised the threat level in Britain from moderate to substantial.
Two separate hauls of weapons were discovered in Carnfunnock and Capanagh parks within three months of each other.
Police said four barrels were unearthed at Carnfunnock - two were empty but two contained a variety of bomb-making components, including wiring, toggle switches, circuit boards, partially constructed timer power units, ball bearings and a small quantity of explosives.
An armour-piercing improvised rocket and two anti-personnel mines were among the cache recovered at Capanagh in May.
Several pipe bombs, magazines and ammunition for an assault rifle, and bomb component parts and command wires were also concealed in barrels in purpose-built holes in woodland.
Larne is predominantly unionist/loyalist, so the finds led to initial speculation that they could be linked to loyalist paramilitaries. However, after assessing the weaponry, police concluded they most likely belonged to dissident republicans.
Maxwell has been detained in custody for another week.
A Metropolitan Police spokeswoman said: "We have a warrant for a further detention from a court for seven days."