There are reports that the main suspect in the the kidnapping and torture of Kevin Lunney has died.
Searches continue to be carried out on both sides of the Border, including in Cavan, as well as the search in Derbyshire as part of the investigation of the abduction of Quinn Industrial Holdings executive.
The man took ill when police were searching his home in Derbyshire, England this morning.
Gardaí and the PSNI have formally launched a joint investigation into the ongoing intimidation against QIH Directors.
"These (attacks) have been obviously a subject of public concern lately and we want to be seen to act in a strong and robust way to show that there's no room for criminality anywhere on the island of Ireland and that as police services we are cooperating in the strongest fashion possible to bring the perpetrators to justice", he said.
The man in his 50s is believed to be one of the main suspects involved in the attack on Mr Lunney in September.
The gang took Mr. Lunney across the border where they viciously assaulted him, breaking one of his legs, slicing his face with a blade and carving the letters QIH on his chest before pouring bleach over him.
The 50-year-old father-of-six was found bleeding on a roadside in Cornfean after being abducted outside his home in Derrylin.
Meanwhile, the directors of Quinn Industrial Holdings have rejected an offer to meet members of the Quinn family, the Irish News has reported.
As well as the operation in Derbyshire, five locations in Co Cavan, three locations in Co Longford and four locations in Dublin are also being searched.
Police on both sides of the border are under pressure to get results, following a long-running series of threats and other incidents.
As part of the latest police operation, PSNI are undertaking five searches in Derrylin, County Fermanagh, while in England police in Derbyshire are also conducting a search operation.
Gardaí said their searches were focused on domestic homes and business premises.