Three people were still being questioned last night in connection with the discovery of Semtex, detonators, handguns and ammunition in west Belfast.
The seizure was made at a house on Ballymurphy Road last Thursday.
A 45-year-old man arrested in Sunderland in the north-east of England on Sunday morning has been flown to Northern Ireland for questioning.
A 21-year-old woman and 29-year-old man held in west Belfast on the same day were also still being questioned last night.
A 67-year-old man and a 38-year-old woman arrested on Thursday were later released pending a report to the Public Prosecution Service.
It is understood some of those to have been questioned are members of the same family.
Police previously said the operation was part of an investigation into "violent dissident terrorist activity".
While it is thought the material belongs to the group calling itself 'the IRA', people locally have expressed surprise at the arrest of some people who would have affiliation to dissident republicans.
