Four men have been arrested after the discovery of a diesel laundering plant in the Jonesborough area of Co Armagh.
The four men from Armagh were questioned and released on bail as investigations continue.
The plant, which was discovered in a farm shed, had the capacity to produce over 4.3m litres of fuel a year.
Three tonnes of toxic waste were found at the location.
A 20ft truck, two cars, pumps and other equipment were also seized.
HMRC Assistant Director Criminal Investigation John Whiting said: "Buying illicit fuel not only funds crime but supports and encourages these dangerous activities within our communities.
"The only winners are the criminals, who are profiting at the expense of honest businesses and endangering the future viability of our legitimate fuel retail service."