When the men were arrested, gardai found they had replica police uniforms, two-way radio sets, pick-axe handles, sledgehammers, plastic ties, balaclavas and gloves.
It was not clear whether the men were planning an action authorized by the IRA or operating independently, but the arrests have added to the pressure on Sinn Fein as a result of the spying allegations in Northern Ireland.
“It appears some sort of major crime was planned, but we are not clear whether it was an abduction or a kidnapping or some sort of robbery,” a Garda source said.
All were arrested under the Offenses Against the State anti-terrorist laws that allowed them to be held for 72 hours without charge.
Amid tight security, they were brought before a special sitting of the three-judge, no-jury Special Criminal Court on Sunday. They were charged with membership in an illegal organization and are still being detained.
A number of the men are understood to have worked as Sinn Fein political activists in the May general election.
The five are Thomas Gilson, 22, of Jobstown, Tallaght; Patrick Brennan, 38, of Clondalkin; Sean O’Donnell, 30, of Sandymount; Stephen Birney, 28, of Clontarf, and John Troy, 20, of Dublin.