Two men, arrested near Dundalk as part of the investigation into, but not directly linked to, the murder of Detective Garda Adrian Donohoe, have been released without charge.
Det Garda Donohoe was shot dead last month during an armed robbery in a credit union in Co Louth.
Gardaí say investigations are ongoing.
The men, aged in their 30s and 70s, were arrested at a house near Dundalk as gardaí carried out six separate searches.
The two men were arrested by detectives probing criminal activity close to the border.
Six locations were searched during the operation in Dundalk in the early hours of the morning last week.
A Garda spokesman said units targeted criminal and subversive activity in the area.
The men are detained under Section 30 of the Offences Against the State Act 1939 at Drogheda Garda Station.
Gardai said the operation is not directly related to the investigation into the murder of Detective Garda Adrian Donohoe.
Detective Donohoe, 41, was shot in the head as he approached a five-strong gang in the grounds of his local credit union in the village of Jenkinstown, Co Louth, on Friday January 25.
A Garda source revealed that teams of officers dedicated to investigating the murder are uncovering other criminal activity in the border area, which led to the latest arrests.
Within the first two weeks of the murder probe, gardai had taken hundreds of statements, opened more than 1,100 lines of inquiry, recorded more than 300 exhibits and seized 140 pieces of CCTV.
“This search and arrest operation this morning was in relation to other criminal activity,” a senior source said. “We expect more of these in the future.”