Belfast, Northern Ireland (CNN) -- Police in the Republic of Ireland released one man but were continuing to question four suspected IRA dissidents after the discovery of what officers described as "a bomb-making factory," they said Thursday.
Police said searches were continuing at a remote farm 40 miles from Dublin in County Kildare where metal tubes and other components were found Wednesday.
Police said they suspect the dissident group Oglaigh na hEireann (Irish Volunteers) was making mortar bombs to be used in Northern Ireland.
Forensic tests were being carried out, police said.
The suspects were being held under Section 30 of the Offenses Against the State Act.
They can be detained for up to three days before being charged or released.
The new head of the Irish police, Commissioner Martin Callinan, this week said tackling dissident republican activity is one of his top priorities.
Dissident republicans are those who want Northern Ireland to be Irish rather than British, and do not accept the 1998 peace deal that largely ended decades of violence in the province.