A Sinn Féin member has been expelled from the party after her partner was arrested as part of the garda investigation into far-right extremism.
The man is still being detained under Section 30 of the Offences Against the State Act.
He was arrested yesterday morning by officers from the Special Detective Unit investigating cross-border terrorism.
Two other men who were charged with possession and control of explosives were remanded in custody after they appeared in court last week.
The court heard that a "violent" right-wing extremist group threatened on video to attack a Galway mosque, IPAS centres and hotels housing migrants around Ireland.
In a statement today, Sinn Féin confirmed "that the partner of a female member of the party had been arrested as part of the investigation into last week's arrest of two alleged far-right extremists".
It said it had been informed last Friday that gardaí had also raided their home as part of the investigation.
It also said "the female party member was expelled from the party on Saturday evening as she failed to notify the party that her home was raided or inform the party about the associated seriousness of this situation".
National Chairperson Declan Kearney praised the "speedy action" of gardaí and said Sinn Féin "will not allow our party to be exposed to any far-right elements".
He also said the far-right has "targeted our party for several years now with death threats, pickets on members' homes and offices and more recently violent actions" and that Sinn Féin has "worked carefully with gardaí, who have been active and vigilant in the face of these threats".
Sinn Féin confirmed that the former member and her partner were signed into Leinster House on two occasions.
In a statement, the party said: "On 16th July they were signed in by Senator Maria McCormack for a endometriosis debate in the Dáil.
"On 17th June they were signed in by a staff member in Maria McCormack's office, at her request, on the day of a housing protest outside the Dáil."
Sinn Féin TD Matt Carthy said the party takes "these matters extremely seriously".
Speaking outside Leinster House, he said: "As soon as we became aware of what had happened, we convened a meeting of the party leadership, and the decision was made to immediately expel this party member for not informing the party about the fact that her house had been raided."
Mr Carthy said the former party member "was not subject to arrest but her partner was".
He said her partner was not a member of Sinn Féin.
"We take these matters incredibly seriously," he said. "Sinn Féin has been the target of many far-right attacks both online and in person," he said.
"We don't tolerate any party member being associated with these activities."
He said a party member in the same county informed their head office of the raid.
Mr Carthy commended gardaí for "ultimately saving lives".
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Additional reporting Róisín Cullen
