A man originally from Northern Ireland is one of nine men being questioned after a suspected dissident republican training camp was uncovered in the Irish Republic.
Gardai cordoned off the forest area
The camp was discovered in a forest close to the Tipperary and Waterford border, according to the Irish police, the Garda Siochana.
The arrested men are alleged to be aligned with banned dissident republican organisation Continuity IRA.
A police spokesman told BBC News the uncovering of the alleged training camp was "significant".
Gardai extended the time limit for questioning the men for another 24 hours on Monday.
They were initially arrested on Sunday under Irish anti-terrorist legislation which permits suspects to be kept in custody for up to 72 hours before being either charged or released.
Firearms, a quantity of ammunition and other paramilitary equipment were seized near the alleged training camp, which remains sealed off.
The men being questioned ranged from late teens to early forties in age and mostly came from the Waterford, Wexford and Limerick areas.
A 10-year-old boy who was at the camp is believed to be related to one of the men.
Police spokesman Garda Superintendent John Farrelly said the site was an isolated area in the south-east of Ireland, about 150 miles from Dublin.
He said from a "cursory look" at the site, there were a number of targets positioned against trees in a clearing in the forest, as well as spent rounds of ammunition.
"It is part of the investigation to establish exactly what went on there."
Police said the operation was continuing at several sites.
The find was made as part of an ongoing operation by the Garda's National Surveillance Unit on the borders of Counties Waterford and Tipperary.
The BBC's Ireland correspondent Kevin Connolly said the discovery of the camp was a reminder of the constant threat to the peace process.