The terrorist arms were found in the Co Fermanagh village of Kinawley near the Irish border.
The police operation has been ongoing for three days with officers conducting forensic searches of farm buildings in the area.
A 43-year-old man arrested in Kinawley on Wednesday remained in police custody tonight after police were granted a further three days to question him.
A 35-year-old man detained in north Belfast in connection with the operation has been released unconditionally.
Detective Chief Inspector Gillian Kearney from the Police Service of Northern Ireland’s Serious Crime Branch said: “During the ongoing operation in Kinawley a significant quantity of explosives, munitions and other related material has been recovered for examination and the operation is continuing.”
Earlier today PSNI Chief Constable George Hamilton said the operation had thwarted “serious harm” being inflicted by dissident republicans.
“We believe we have prevented serious harm being caused to our communities and I welcome the efforts by my colleagues in the crime operations department,” he said
He added: “We do believe that violent dissident republicans are behind this activity in Fermanagh.”