Police in the Irish Republic are examining 30 boxes of business documents seized during raids focusing on organised crime in the border area.
Irish police seal off a road in County Louth
Garda Superintendent Kevin Donohoe said nine sites in County Louth were searched and PSNI officers conducted raids in south Armagh on Thursday.
He said they hoped to glean enough information from documents and seized computers to advance their inquiries.
"We would be very hopeful they would yield sufficient evidence," he said.
The searches focused on businesses and homes in the Hacksballscross area, which straddles the border.
One of the properties searched was a farm in south Armagh associated with Thomas 'Slab' Murphy, who is widely reported to be the IRA's Chief of Staff.
Mr Donohoe said the operation was targeting fuel and cigarette smuggling as well as money and fuel laundering, which "generated massive, massive profits" for those involved.
A number of vehicles, 8,000 litres of fuel, two shotguns and ammunition were also seized during the raids.
Three people arrested during the operation by Irish police were released.
Mr Donohoe said they were not linking the raids to any previous operation and that they were not targeting any paramilitary group in particular.
"Our sole focus was looking at a very professional extensive organised crime operation in the north Louth/south Armagh area," he said.
"The investigation will take us wherever it takes us."