A 43-year-old man was arrested in Derry this morning, Thursday 8th August, under the Terrorism Act.
He has been taken to Musgrave Serious Crime Suite in Belfast for questioning.
The man has been arrested in connection with an ongoing investigation following an undercover surveillance operation by the security forces in the city on Tuesday, May 21 which resulted in the seizure of an AKM firearm and a quantity of ammunition.
This is the fourth arrest in relation to the investigation.
Two men aged 56 and 59 have since been charged to court and remanded in custody.
A 24-year-old man, arrested in June, was later released following questioning.