A man is being questioned at Letterkenny Garda station after he was arrested for allegedly being a member of an unlawful organisation.
The man is understood to be in his 30s and from the North of Ireland.
He was arrested in east Donegal on Monday but Gardai have not identified the specific location.
He was arrested under Section 30 of the 1939 Offences Against The State Act.
He was taken to Letterkenny Garda station where he is being quizzed by detectives.
A Garda spokesperson confirmed: “The investigation is ongoing. No further information is available at this time.”
